diff --git a/.rubocop/cop/zammad/no_to_sym_on_string.rb b/.rubocop/cop/zammad/no_to_sym_on_string.rb
new file mode 100644
index 000000000..fd122a9cd
--- /dev/null
+++ b/.rubocop/cop/zammad/no_to_sym_on_string.rb
@@ -0,0 +1,40 @@
+module RuboCop
+  module Cop
+    module Zammad
+      # This cop is used to identify usages of `.to_sym` on Strings and
+      # changes them to use the `:` prefix instead.
+      #
+      # @example
+      #   # bad
+      #   "a-Symbol".to_sym
+      #   'a-Symbol'.to_sym
+      #   "a-#{'Symbol'}".to_sym
+      #
+      #   # good
+      #   :"a-Symbol"
+      #   :'a-Symbol'
+      #   :"a-#{'Symbol'}"
+      class NoToSymOnString < Base
+        extend AutoCorrector
+
+        def_node_matcher :to_sym?, <<-PATTERN
+          {
+            $(send (str ...) :to_sym ...)
+            $(send (dstr ...) :to_sym ...)
+          }
+        PATTERN
+
+        MSG = "Don't use `.to_sym` on String. Prefer `:` prefix instead.".freeze
+
+        def on_send(node)
+          result = *to_sym?(node)
+          return if result.empty?
+
+          add_offense(node, message: MSG) do |corrector|
+            corrector.replace(node, ":#{result.first.source}")
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/.rubocop/rubocop_zammad.rb b/.rubocop/rubocop_zammad.rb
index 552e9f0b5..fdf882167 100644
--- a/.rubocop/rubocop_zammad.rb
+++ b/.rubocop/rubocop_zammad.rb
@@ -1,2 +1,3 @@
 require_relative 'cop/zammad/exists_condition'
+require_relative 'cop/zammad/no_to_sym_on_string'
 require_relative 'cop/zammad/prefer_negated_if_over_unless'
diff --git a/app/models/channel/email_parser.rb b/app/models/channel/email_parser.rb
index 76f1ae6a8..c466723b2 100644
--- a/app/models/channel/email_parser.rb
+++ b/app/models/channel/email_parser.rb
@@ -158,7 +158,7 @@ returns
     end
 
     # check ignore header
-    if mail['x-zammad-ignore'.to_sym] == 'true' || mail['x-zammad-ignore'.to_sym] == true
+    if mail[:'x-zammad-ignore'] == 'true' || mail[:'x-zammad-ignore'] == true
       Rails.logger.info "ignored email with msgid '#{mail[:message_id]}' from '#{mail[:from]}' because of x-zammad-ignore header"
       return
     end
@@ -174,7 +174,7 @@ returns
     Transaction.execute(interface_handle: "#{original_interface_handle}.postmaster") do
 
       # get sender user
-      session_user_id = mail['x-zammad-session-user-id'.to_sym]
+      session_user_id = mail[:'x-zammad-session-user-id']
       if !session_user_id
         raise 'No x-zammad-session-user-id, no sender set!'
       end
@@ -188,11 +188,11 @@ returns
       UserInfo.current_user_id = session_user.id
 
       # get ticket# based on email headers
-      if mail['x-zammad-ticket-id'.to_sym]
-        ticket = Ticket.find_by(id: mail['x-zammad-ticket-id'.to_sym])
+      if mail[:'x-zammad-ticket-id']
+        ticket = Ticket.find_by(id: mail[:'x-zammad-ticket-id'])
       end
-      if mail['x-zammad-ticket-number'.to_sym]
-        ticket = Ticket.find_by(number: mail['x-zammad-ticket-number'.to_sym])
+      if mail[:'x-zammad-ticket-number']
+        ticket = Ticket.find_by(number: mail[:'x-zammad-ticket-number'])
       end
 
       # set ticket state to open if not new
@@ -203,9 +203,9 @@ returns
         ticket.save! if ticket.has_changes_to_save?
 
         # set ticket to open again or keep create state
-        if !mail['x-zammad-ticket-followup-state'.to_sym] && !mail['x-zammad-ticket-followup-state_id'.to_sym]
+        if !mail[:'x-zammad-ticket-followup-state'] && !mail[:'x-zammad-ticket-followup-state_id']
           new_state = Ticket::State.find_by(default_create: true)
-          if ticket.state_id != new_state.id && !mail['x-zammad-out-of-office'.to_sym]
+          if ticket.state_id != new_state.id && !mail[:'x-zammad-out-of-office']
             ticket.state = Ticket::State.find_by(default_follow_up: true)
             ticket.save!
           end
@@ -250,8 +250,8 @@ returns
       end
 
       # apply tags to ticket
-      if mail['x-zammad-ticket-tags'.to_sym].present?
-        mail['x-zammad-ticket-tags'.to_sym].each do |tag|
+      if mail[:'x-zammad-ticket-tags'].present?
+        mail[:'x-zammad-ticket-tags'].each do |tag|
           ticket.tag_add(tag)
         end
       end
diff --git a/app/models/channel/filter/auto_response_check.rb b/app/models/channel/filter/auto_response_check.rb
index 9fec214c6..ad04e049a 100644
--- a/app/models/channel/filter/auto_response_check.rb
+++ b/app/models/channel/filter/auto_response_check.rb
@@ -5,34 +5,34 @@ module Channel::Filter::AutoResponseCheck
   def self.run(_channel, mail)
 
     # if header is available, do not generate auto response
-    mail[ 'x-zammad-send-auto-response'.to_sym ] = false
-    mail[ 'x-zammad-is-auto-response'.to_sym ] = true
+    mail[ :'x-zammad-send-auto-response' ] = false
+    mail[ :'x-zammad-is-auto-response' ] = true
 
-    if !mail[ 'x-zammad-article-preferences'.to_sym ]
-      mail[ 'x-zammad-article-preferences'.to_sym ] = {}
+    if !mail[ :'x-zammad-article-preferences' ]
+      mail[ :'x-zammad-article-preferences' ] = {}
     end
-    mail[ 'x-zammad-article-preferences'.to_sym ]['send-auto-response'] = false
-    mail[ 'x-zammad-article-preferences'.to_sym ]['is-auto-response'] = true
+    mail[ :'x-zammad-article-preferences' ]['send-auto-response'] = false
+    mail[ :'x-zammad-article-preferences' ]['is-auto-response'] = true
 
     # do not send an auto response if one of the following headers exists
-    return if mail[ 'list-unsubscribe'.to_sym ] && mail[ 'list-unsubscribe'.to_sym ] =~ /.../
-    return if mail[ 'x-loop'.to_sym ] && mail[ 'x-loop'.to_sym ] =~ /(yes|true)/i
-    return if mail[ 'precedence'.to_sym ] && mail[ 'precedence'.to_sym ] =~ /(bulk|list|junk)/i
-    return if mail[ 'auto-submitted'.to_sym ] && mail[ 'auto-submitted'.to_sym ] =~ /auto-(generated|replied)/i
-    return if mail[ 'x-auto-response-suppress'.to_sym ] && mail[ 'x-auto-response-suppress'.to_sym ] =~ /all/i
+    return if mail[ :'list-unsubscribe' ] && mail[ :'list-unsubscribe' ] =~ /.../
+    return if mail[ :'x-loop' ] && mail[ :'x-loop' ] =~ /(yes|true)/i
+    return if mail[ :precedence ] && mail[ :precedence ] =~ /(bulk|list|junk)/i
+    return if mail[ :'auto-submitted' ] && mail[ :'auto-submitted' ] =~ /auto-(generated|replied)/i
+    return if mail[ :'x-auto-response-suppress' ] && mail[ :'x-auto-response-suppress' ] =~ /all/i
 
     # do not send an auto response if sender is system itself
-    message_id = mail[ 'message_id'.to_sym ]
+    message_id = mail[ :message_id ]
     if message_id
       fqdn = Setting.get('fqdn')
       return if message_id.match?(/@#{Regexp.quote(fqdn)}/i)
     end
 
-    mail[ 'x-zammad-send-auto-response'.to_sym ] = true
-    mail[ 'x-zammad-is-auto-response'.to_sym ] = false
+    mail[ :'x-zammad-send-auto-response' ] = true
+    mail[ :'x-zammad-is-auto-response' ] = false
 
-    mail[ 'x-zammad-article-preferences'.to_sym ]['send-auto-response'] = true
-    mail[ 'x-zammad-article-preferences'.to_sym ]['is-auto-response'] = false
+    mail[ :'x-zammad-article-preferences' ]['send-auto-response'] = true
+    mail[ :'x-zammad-article-preferences' ]['is-auto-response'] = false
 
   end
 end
diff --git a/app/models/channel/filter/bounce_delivery_temporary_failed.rb b/app/models/channel/filter/bounce_delivery_temporary_failed.rb
index 9d07b6cb4..5a74b0fcd 100644
--- a/app/models/channel/filter/bounce_delivery_temporary_failed.rb
+++ b/app/models/channel/filter/bounce_delivery_temporary_failed.rb
@@ -10,7 +10,7 @@ module Channel::Filter::BounceDeliveryTemporaryFailed
     return if mail[:mail_instance].error_status != '4.4.1'
 
     # if header is available, do change current ticket state
-    mail['x-zammad-out-of-office'.to_sym] = true
+    mail[:'x-zammad-out-of-office'] = true
 
     true
   end
diff --git a/app/models/channel/filter/bounce_follow_up_check.rb b/app/models/channel/filter/bounce_follow_up_check.rb
index 0aa26ec1f..1ee32d27d 100644
--- a/app/models/channel/filter/bounce_follow_up_check.rb
+++ b/app/models/channel/filter/bounce_follow_up_check.rb
@@ -7,7 +7,7 @@ module Channel::Filter::BounceFollowUpCheck
     return if !mail[:mail_instance]
     return if !mail[:mail_instance].bounced?
     return if !mail[:attachments]
-    return if mail[ 'x-zammad-ticket-id'.to_sym ]
+    return if mail[ :'x-zammad-ticket-id' ]
 
     mail[:attachments].each do |attachment|
       next if !attachment[:preferences]
@@ -22,8 +22,8 @@ module Channel::Filter::BounceFollowUpCheck
       next if !article
 
       Rails.logger.debug { "Follow-up for '##{article.ticket.number}' in bounce email." }
-      mail[ 'x-zammad-ticket-id'.to_sym ] = article.ticket_id
-      mail[ 'x-zammad-is-auto-response'.to_sym ] = true
+      mail[ :'x-zammad-ticket-id' ] = article.ticket_id
+      mail[ :'x-zammad-is-auto-response' ] = true
 
       return true
     end
diff --git a/app/models/channel/filter/follow_up_check.rb b/app/models/channel/filter/follow_up_check.rb
index f0c048549..3d5db3408 100644
--- a/app/models/channel/filter/follow_up_check.rb
+++ b/app/models/channel/filter/follow_up_check.rb
@@ -4,13 +4,13 @@ module Channel::Filter::FollowUpCheck
 
   def self.run(_channel, mail)
 
-    return if mail['x-zammad-ticket-id'.to_sym]
+    return if mail[:'x-zammad-ticket-id']
 
     # get ticket# from subject
     ticket = Ticket::Number.check(mail[:subject])
     if ticket
       Rails.logger.debug { "Follow-up for '##{ticket.number}' in subject." }
-      mail['x-zammad-ticket-id'.to_sym] = ticket.id
+      mail[:'x-zammad-ticket-id'] = ticket.id
       return true
     end
 
@@ -21,7 +21,7 @@ module Channel::Filter::FollowUpCheck
       ticket = Ticket::Number.check(mail[:body].html2text)
       if ticket
         Rails.logger.debug { "Follow-up for '##{ticket.number}' in body." }
-        mail['x-zammad-ticket-id'.to_sym] = ticket.id
+        mail[:'x-zammad-ticket-id'] = ticket.id
         return true
       end
     end
@@ -49,24 +49,24 @@ module Channel::Filter::FollowUpCheck
         next if !ticket
 
         Rails.logger.debug { "Follow-up for '##{ticket.number}' in attachment." }
-        mail['x-zammad-ticket-id'.to_sym] = ticket.id
+        mail[:'x-zammad-ticket-id'] = ticket.id
         return true
       end
     end
 
     # get ticket# from references
-    if setting.include?('references') || (mail['x-zammad-is-auto-response'.to_sym] == true || Setting.get('ticket_hook_position') == 'none')
+    if setting.include?('references') || (mail[:'x-zammad-is-auto-response'] == true || Setting.get('ticket_hook_position') == 'none')
 
       # get all references 'References' + 'In-Reply-To'
       references = ''
       if mail[:references]
         references += mail[:references]
       end
-      if mail['in-reply-to'.to_sym]
+      if mail[:'in-reply-to']
         if references != ''
           references += ' '
         end
-        references += mail['in-reply-to'.to_sym]
+        references += mail[:'in-reply-to']
       end
       if references != ''
         message_ids = references.split(/\s+/)
@@ -76,7 +76,7 @@ module Channel::Filter::FollowUpCheck
           next if !article
 
           Rails.logger.debug { "Follow-up for '##{article.ticket.number}' in references." }
-          mail['x-zammad-ticket-id'.to_sym] = article.ticket_id
+          mail[:'x-zammad-ticket-id'] = article.ticket_id
           return true
         end
       end
@@ -90,11 +90,11 @@ module Channel::Filter::FollowUpCheck
       if mail[:references]
         references += mail[:references]
       end
-      if mail['in-reply-to'.to_sym]
+      if mail[:'in-reply-to']
         if references != ''
           references += ' '
         end
-        references += mail['in-reply-to'.to_sym]
+        references += mail[:'in-reply-to']
       end
       if references != ''
         message_ids = references.split(/\s+/)
@@ -117,7 +117,7 @@ module Channel::Filter::FollowUpCheck
           next if subject_to_check != article_first.subject
 
           Rails.logger.debug { "Follow-up for '##{article.ticket.number}' in references with same subject as inital article." }
-          mail['x-zammad-ticket-id'.to_sym] = article_first.ticket_id
+          mail[:'x-zammad-ticket-id'] = article_first.ticket_id
           return true
         end
       end
diff --git a/app/models/channel/filter/follow_up_possible_check.rb b/app/models/channel/filter/follow_up_possible_check.rb
index e4f639c13..b9376f72c 100644
--- a/app/models/channel/filter/follow_up_possible_check.rb
+++ b/app/models/channel/filter/follow_up_possible_check.rb
@@ -3,7 +3,7 @@
 module Channel::Filter::FollowUpPossibleCheck
 
   def self.run(_channel, mail)
-    ticket_id = mail['x-zammad-ticket-id'.to_sym]
+    ticket_id = mail[:'x-zammad-ticket-id']
     return true if !ticket_id
 
     ticket = Ticket.lookup(id: ticket_id)
@@ -13,9 +13,9 @@ module Channel::Filter::FollowUpPossibleCheck
     # in case of closed tickets, remove follow-up information
     case ticket.group.follow_up_possible
     when 'new_ticket'
-      mail[:subject]                        = ticket.subject_clean(mail[:subject])
-      mail['x-zammad-ticket-id'.to_sym]     = nil
-      mail['x-zammad-ticket-number'.to_sym] = nil
+      mail[:subject] = ticket.subject_clean(mail[:subject])
+      mail[:'x-zammad-ticket-id']     = nil
+      mail[:'x-zammad-ticket-number'] = nil
     end
 
     true
diff --git a/app/models/channel/filter/identify_sender.rb b/app/models/channel/filter/identify_sender.rb
index a1b7499dc..8a0345f00 100644
--- a/app/models/channel/filter/identify_sender.rb
+++ b/app/models/channel/filter/identify_sender.rb
@@ -4,7 +4,7 @@ module Channel::Filter::IdentifySender
 
   def self.run(_channel, mail)
 
-    customer_user_id = mail[ 'x-zammad-ticket-customer_id'.to_sym ]
+    customer_user_id = mail[ :'x-zammad-ticket-customer_id' ]
     customer_user = nil
     if customer_user_id.present?
       customer_user = User.lookup(id: customer_user_id)
@@ -16,20 +16,20 @@ module Channel::Filter::IdentifySender
     end
 
     # check if sender exists in database
-    if !customer_user && mail[ 'x-zammad-customer-login'.to_sym ].present?
-      customer_user = User.find_by(login: mail[ 'x-zammad-customer-login'.to_sym ])
+    if !customer_user && mail[ :'x-zammad-customer-login' ].present?
+      customer_user = User.find_by(login: mail[ :'x-zammad-customer-login' ])
     end
-    if !customer_user && mail[ 'x-zammad-customer-email'.to_sym ].present?
-      customer_user = User.find_by(email: mail[ 'x-zammad-customer-email'.to_sym ])
+    if !customer_user && mail[ :'x-zammad-customer-email' ].present?
+      customer_user = User.find_by(email: mail[ :'x-zammad-customer-email' ])
     end
 
     # get correct customer
     if !customer_user && Setting.get('postmaster_sender_is_agent_search_for_customer') == true
-      if mail[ 'x-zammad-ticket-create-article-sender'.to_sym ] == 'Agent'
+      if mail[ :'x-zammad-ticket-create-article-sender' ] == 'Agent'
 
         # get first recipient and set customer
         begin
-          to = 'raw-to'.to_sym
+          to = :'raw-to'
           if mail[to]&.addrs
             items = mail[to].addrs
             items.each do |item|
@@ -54,18 +54,18 @@ module Channel::Filter::IdentifySender
     # take regular from as customer
     if !customer_user
       customer_user = user_create(
-        login:     mail[ 'x-zammad-customer-login'.to_sym ] || mail[ 'x-zammad-customer-email'.to_sym ] || mail[:from_email],
-        firstname: mail[ 'x-zammad-customer-firstname'.to_sym ] || mail[:from_display_name],
-        lastname:  mail[ 'x-zammad-customer-lastname'.to_sym ],
-        email:     mail[ 'x-zammad-customer-email'.to_sym ] || mail[:from_email],
+        login:     mail[ :'x-zammad-customer-login' ] || mail[ :'x-zammad-customer-email' ] || mail[:from_email],
+        firstname: mail[ :'x-zammad-customer-firstname' ] || mail[:from_display_name],
+        lastname:  mail[ :'x-zammad-customer-lastname' ],
+        email:     mail[ :'x-zammad-customer-email' ] || mail[:from_email],
       )
     end
 
     create_recipients(mail)
-    mail[ 'x-zammad-ticket-customer_id'.to_sym ] = customer_user.id
+    mail[ :'x-zammad-ticket-customer_id' ] = customer_user.id
 
     # find session user
-    session_user_id = mail[ 'x-zammad-session-user-id'.to_sym ]
+    session_user_id = mail[ :'x-zammad-session-user-id' ]
     session_user = nil
     if session_user_id.present?
       session_user = User.lookup(id: session_user_id)
@@ -84,7 +84,7 @@ module Channel::Filter::IdentifySender
       )
     end
     if session_user
-      mail[ 'x-zammad-session-user-id'.to_sym ] = session_user.id
+      mail[ :'x-zammad-session-user-id' ] = session_user.id
     end
 
     true
diff --git a/app/models/channel/filter/monitoring_base.rb b/app/models/channel/filter/monitoring_base.rb
index b342986ef..ec36b68da 100644
--- a/app/models/channel/filter/monitoring_base.rb
+++ b/app/models/channel/filter/monitoring_base.rb
@@ -24,7 +24,7 @@ class Channel::Filter::MonitoringBase
     return if mail[:from].blank?
     return if mail[:body].blank?
 
-    session_user_id = mail[ 'x-zammad-session-user-id'.to_sym ]
+    session_user_id = mail[ :'x-zammad-session-user-id' ]
     return if !session_user_id
 
     # check if sender is monitoring
@@ -94,40 +94,40 @@ class Channel::Filter::MonitoringBase
       next if ticket.preferences[integration]['service'] != result['service']
 
       # found open ticket for service+host
-      mail[ 'x-zammad-ticket-id'.to_sym ] = ticket.id
+      mail[ :'x-zammad-ticket-id' ] = ticket.id
 
       # check if service is recovered
       if auto_close && result['state'].present? && result['state'].match(/#{state_recovery_match}/i)
         Rails.logger.info "MonitoringBase.#{integration} set autoclose to state_id #{auto_close_state_id}"
         state = Ticket::State.lookup(id: auto_close_state_id)
         if state
-          mail[ 'x-zammad-ticket-followup-state'.to_sym ] = state.name
+          mail[ :'x-zammad-ticket-followup-state' ] = state.name
         end
       end
       return true
     end
 
     # new ticket, set meta data
-    if !mail[ 'x-zammad-ticket-id'.to_sym ]
-      if !mail[ 'x-zammad-ticket-preferences'.to_sym ]
-        mail[ 'x-zammad-ticket-preferences'.to_sym ] = {}
+    if !mail[ :'x-zammad-ticket-id' ]
+      if !mail[ :'x-zammad-ticket-preferences' ]
+        mail[ :'x-zammad-ticket-preferences' ] = {}
       end
       preferences = {}
       preferences[integration] = result
       preferences.each do |key, value|
-        mail[ 'x-zammad-ticket-preferences'.to_sym ][key] = value
+        mail[ :'x-zammad-ticket-preferences' ][key] = value
       end
     end
 
     # ignore states
     if state_ignore_match.present? && result['state'].present? && result['state'].match(/#{state_ignore_match}/i)
-      mail[ 'x-zammad-ignore'.to_sym ] = true
+      mail[ :'x-zammad-ignore' ] = true
       return true
     end
 
     # if now problem exists, just ignore the email
     if result['state'].present? && result['state'].match(/#{state_recovery_match}/i)
-      mail[ 'x-zammad-ignore'.to_sym ] = true
+      mail[ :'x-zammad-ignore' ] = true
       return true
     end
 
diff --git a/app/models/channel/filter/out_of_office_check.rb b/app/models/channel/filter/out_of_office_check.rb
index 9d1b41078..505bdab00 100644
--- a/app/models/channel/filter/out_of_office_check.rb
+++ b/app/models/channel/filter/out_of_office_check.rb
@@ -4,32 +4,32 @@ module Channel::Filter::OutOfOfficeCheck
 
   def self.run(_channel, mail)
 
-    mail[ 'x-zammad-out-of-office'.to_sym ] = false
+    mail[ :'x-zammad-out-of-office' ] = false
 
     # check ms out of office characteristics
-    if mail[ 'x-auto-response-suppress'.to_sym ]
-      return if !mail[ 'x-auto-response-suppress'.to_sym ].match?(/all/i)
-      return if !mail[ 'x-ms-exchange-inbox-rules-loop'.to_sym ]
+    if mail[ :'x-auto-response-suppress' ]
+      return if !mail[ :'x-auto-response-suppress' ].match?(/all/i)
+      return if !mail[ :'x-ms-exchange-inbox-rules-loop' ]
 
-      mail[ 'x-zammad-out-of-office'.to_sym ] = true
+      mail[ :'x-zammad-out-of-office' ] = true
       return
     end
 
-    if mail[ 'auto-submitted'.to_sym ]
+    if mail[ :'auto-submitted' ]
 
       # check zimbra out of office characteristics
-      if mail[ 'auto-submitted'.to_sym ].match?(/vacation/i)
-        mail[ 'x-zammad-out-of-office'.to_sym ] = true
+      if mail[ :'auto-submitted' ].match?(/vacation/i)
+        mail[ :'x-zammad-out-of-office' ] = true
       end
 
       # check cloud out of office characteristics
-      if mail[ 'auto-submitted'.to_sym ].match?(/auto-replied;\sowner-email=/i)
-        mail[ 'x-zammad-out-of-office'.to_sym ] = true
+      if mail[ :'auto-submitted' ].match?(/auto-replied;\sowner-email=/i)
+        mail[ :'x-zammad-out-of-office' ] = true
       end
 
       # gmail check out of office characteristics
-      if mail[ 'auto-submitted'.to_sym ] =~ /auto-replied/i && mail[ 'subject'.to_sym ] =~ /vacation/i
-        mail[ 'x-zammad-out-of-office'.to_sym ] = true
+      if mail[ :'auto-submitted' ] =~ /auto-replied/i && mail[ :subject ] =~ /vacation/i
+        mail[ :'x-zammad-out-of-office' ] = true
       end
 
       return
diff --git a/app/models/channel/filter/own_notification_loop_detection.rb b/app/models/channel/filter/own_notification_loop_detection.rb
index 8e4d12477..8bdc71669 100644
--- a/app/models/channel/filter/own_notification_loop_detection.rb
+++ b/app/models/channel/filter/own_notification_loop_detection.rb
@@ -4,17 +4,17 @@ module Channel::Filter::OwnNotificationLoopDetection
 
   def self.run(_channel, mail)
 
-    message_id = mail['message-id'.to_sym]
+    message_id = mail[:'message-id']
     return if !message_id
 
-    recedence = mail['precedence'.to_sym]
+    recedence = mail[:precedence]
     return if !recedence
     return if !recedence.match?(/bulk/i)
 
     fqdn = Setting.get('fqdn')
     return if !message_id.match?(/@#{Regexp.quote(fqdn)}>/i)
 
-    mail[ 'x-zammad-ignore'.to_sym ] = true
+    mail[ :'x-zammad-ignore' ] = true
     Rails.logger.info "Detected own sent notification mail and dropped it to prevent loops (message_id: #{message_id}, from: #{mail[:from]}, to: #{mail[:to]})"
 
   end
diff --git a/app/models/channel/filter/reply_to_based_sender.rb b/app/models/channel/filter/reply_to_based_sender.rb
index 996ee0285..78e2bb0c4 100644
--- a/app/models/channel/filter/reply_to_based_sender.rb
+++ b/app/models/channel/filter/reply_to_based_sender.rb
@@ -4,19 +4,19 @@ module Channel::Filter::ReplyToBasedSender
 
   def self.run(_channel, mail)
 
-    reply_to = mail['reply-to'.to_sym]
+    reply_to = mail[:'reply-to']
     return if reply_to.blank?
 
     setting = Setting.get('postmaster_sender_based_on_reply_to')
     return if setting.blank?
 
     # remember original sender
-    mail['raw-origin_from'.to_sym]          = mail['raw-from'.to_sym]
-    mail['origin_from'.to_sym]              = mail[:from]
-    mail['origin_from_email'.to_sym]        = mail[:from_email]
-    mail['origin_from_local'.to_sym]        = mail[:from_local]
-    mail['origin_from_domain'.to_sym]       = mail[:from_domain]
-    mail['origin_from_display_name'.to_sym] = mail[:from_display_name]
+    mail[:'raw-origin_from']        = mail[:'raw-from']
+    mail[:origin_from]              = mail[:from]
+    mail[:origin_from_email]        = mail[:from_email]
+    mail[:origin_from_local]        = mail[:from_local]
+    mail[:origin_from_domain]       = mail[:from_domain]
+    mail[:origin_from_display_name] = mail[:from_display_name]
 
     # get properties of reply-to header
     result = Channel::EmailParser.sender_attributes(reply_to)
@@ -24,7 +24,7 @@ module Channel::Filter::ReplyToBasedSender
     if setting == 'as_sender_of_email'
 
       # set new sender
-      mail['raw-from'.to_sym]  = mail['raw-reply-to'.to_sym]
+      mail[:'raw-from']        = mail[:'raw-reply-to']
       mail[:from]              = reply_to
       mail[:from_email]        = result[:from_email]
       mail[:from_local]        = result[:from_local]
@@ -36,11 +36,11 @@ module Channel::Filter::ReplyToBasedSender
     if setting == 'as_sender_of_email_use_from_realname'
 
       # set new sender
-      mail['raw-from'.to_sym] = mail['raw-reply-to'.to_sym]
-      mail[:from]             = reply_to
-      mail[:from_email]       = result[:from_email]
-      mail[:from_local]       = result[:from_local]
-      mail[:from_domain]      = result[:from_domain]
+      mail[:'raw-from']  = mail[:'raw-reply-to']
+      mail[:from]        = reply_to
+      mail[:from_email]  = result[:from_email]
+      mail[:from_local]  = result[:from_local]
+      mail[:from_domain] = result[:from_domain]
       return
     end
 
diff --git a/app/models/channel/filter/sender_is_system_address.rb b/app/models/channel/filter/sender_is_system_address.rb
index 495727c36..75fe818fa 100644
--- a/app/models/channel/filter/sender_is_system_address.rb
+++ b/app/models/channel/filter/sender_is_system_address.rb
@@ -5,11 +5,11 @@ module Channel::Filter::SenderIsSystemAddress
   def self.run(_channel, mail)
 
     # if attributes already set by header
-    return if mail['x-zammad-ticket-create-article-sender'.to_sym]
-    return if mail['x-zammad-article-sender'.to_sym]
+    return if mail[:'x-zammad-ticket-create-article-sender']
+    return if mail[:'x-zammad-article-sender']
 
     # check if sender address is system
-    form = 'raw-from'.to_sym
+    form = :'raw-from'
     return if mail[form].blank?
     return if mail[:to].blank?
 
@@ -21,8 +21,8 @@ module Channel::Filter::SenderIsSystemAddress
       items.each do |item|
         next if !EmailAddress.exists?(email: item.address.downcase)
 
-        mail['x-zammad-ticket-create-article-sender'.to_sym] = 'Agent'
-        mail['x-zammad-article-sender'.to_sym] = 'Agent'
+        mail[:'x-zammad-ticket-create-article-sender'] = 'Agent'
+        mail[:'x-zammad-article-sender']               = 'Agent'
         return true
       end
     rescue => e
@@ -37,18 +37,18 @@ module Channel::Filter::SenderIsSystemAddress
       return if !user
       return if !user.permissions?('ticket.agent')
 
-      mail['x-zammad-ticket-create-article-sender'.to_sym] = 'Agent'
-      mail['x-zammad-article-sender'.to_sym]               = 'Agent'
+      mail[:'x-zammad-ticket-create-article-sender'] = 'Agent'
+      mail[:'x-zammad-article-sender']               = 'Agent'
 
       # if the agent is also customer of the ticket then
       # we need to set the sender as customer.
-      ticket_id = mail['x-zammad-ticket-id'.to_sym]
+      ticket_id = mail[:'x-zammad-ticket-id']
       if ticket_id.present?
         ticket = Ticket.lookup(id: ticket_id)
 
         if ticket.present? && ticket.customer_id == user.id
-          mail['x-zammad-ticket-create-article-sender'.to_sym] = 'Customer'
-          mail['x-zammad-article-sender'.to_sym]               = 'Customer'
+          mail[:'x-zammad-ticket-create-article-sender'] = 'Customer'
+          mail[:'x-zammad-article-sender']               = 'Customer'
         end
       end
       return true
diff --git a/app/models/channel/filter/service_now_check.rb b/app/models/channel/filter/service_now_check.rb
index 281ace9d2..3945e0739 100644
--- a/app/models/channel/filter/service_now_check.rb
+++ b/app/models/channel/filter/service_now_check.rb
@@ -80,6 +80,6 @@ returns:
     )
     return if sync_entry.blank?
 
-    mail[ 'x-zammad-ticket-id'.to_sym ] = sync_entry.o_id
+    mail[ :'x-zammad-ticket-id' ] = sync_entry.o_id
   end
 end
diff --git a/app/models/concerns/can_be_published.rb b/app/models/concerns/can_be_published.rb
index cf0bb2b5e..017009ff0 100644
--- a/app/models/concerns/can_be_published.rb
+++ b/app/models/concerns/can_be_published.rb
@@ -32,7 +32,7 @@ module CanBePublished
     after_touch   :update_active_publicly
 
     %i[archived published internal].each do |scope_name|
-      local  = "#{scope_name}_by".to_sym
+      local  = :"#{scope_name}_by"
       remote = inverse_relation_name(scope_name).to_sym
 
       belongs_to local, class_name: 'User', inverse_of: remote, optional: true
diff --git a/app/models/concerns/checks_html_sanitized.rb b/app/models/concerns/checks_html_sanitized.rb
index 5f40caee5..9668cf14d 100644
--- a/app/models/concerns/checks_html_sanitized.rb
+++ b/app/models/concerns/checks_html_sanitized.rb
@@ -19,7 +19,7 @@ module ChecksHtmlSanitized
       next if value.blank?
       next if !sanitizeable?(attribute, value)
 
-      send("#{attribute}=".to_sym, HtmlSanitizer.strict(value))
+      send(:"#{attribute}=", HtmlSanitizer.strict(value))
     end
     true
   end
diff --git a/app/models/concerns/has_agent_allowed_params.rb b/app/models/concerns/has_agent_allowed_params.rb
index d4bd4289f..7a9c55698 100644
--- a/app/models/concerns/has_agent_allowed_params.rb
+++ b/app/models/concerns/has_agent_allowed_params.rb
@@ -19,7 +19,7 @@ module HasAgentAllowedParams
       return [] if !const_defined?(:AGENT_ALLOWED_NESTED_RELATIONS)
 
       const_get(:AGENT_ALLOWED_NESTED_RELATIONS).map do |relation_identifier|
-        key = "#{relation_identifier}_attributes".to_sym
+        key = :"#{relation_identifier}_attributes"
         value = reflect_on_association(relation_identifier).klass.agent_allowed_params
 
         if reflect_on_association(relation_identifier).is_a? ActiveRecord::Reflection::HasManyReflection
diff --git a/app/models/concerns/has_group_relation_definition.rb b/app/models/concerns/has_group_relation_definition.rb
index 78a51d29f..b652f752e 100644
--- a/app/models/concerns/has_group_relation_definition.rb
+++ b/app/models/concerns/has_group_relation_definition.rb
@@ -59,7 +59,7 @@ module HasGroupRelationDefinition
     end
 
     def ref_key
-      @ref_key ||= "#{group_relation_model_identifier}_id".to_sym
+      @ref_key ||= :"#{group_relation_model_identifier}_id"
     end
   end
 end
diff --git a/app/models/concerns/has_groups.rb b/app/models/concerns/has_groups.rb
index 08abd846f..69659fd08 100644
--- a/app/models/concerns/has_groups.rb
+++ b/app/models/concerns/has_groups.rb
@@ -355,7 +355,7 @@ module HasGroups
     #
     # @return [Symbol] The relation identifier
     def group_through_identifier
-      "#{name.downcase}_groups".to_sym
+      :"#{name.downcase}_groups"
     end
 
     def ensure_group_id_parameter(group_or_id)
diff --git a/lib/import/exchange/item_attributes.rb b/lib/import/exchange/item_attributes.rb
index 54b107d80..2a20f2fcf 100644
--- a/lib/import/exchange/item_attributes.rb
+++ b/lib/import/exchange/item_attributes.rb
@@ -87,7 +87,7 @@ module Import
             result_key = if %i[text id].include?(key) && ( !result[result_key] || result[result_key] == value )
                            prefix
                          else
-                           "#{prefix}.#{key}".to_sym
+                           :"#{prefix}.#{key}"
                          end
           end
           result_key = result_key.to_s.downcase
diff --git a/lib/secure_mailing/smime/incoming.rb b/lib/secure_mailing/smime/incoming.rb
index cddc24429..d1624a95d 100644
--- a/lib/secure_mailing/smime/incoming.rb
+++ b/lib/secure_mailing/smime/incoming.rb
@@ -35,7 +35,7 @@ class SecureMailing::SMIME::Incoming < SecureMailing::Backend::Handler
 
   def article_preferences
     @article_preferences ||= begin
-      key = 'x-zammad-article-preferences'.to_sym
+      key = :'x-zammad-article-preferences'
       @mail[ key ] ||= {}
       @mail[ key ]
     end
diff --git a/lib/sequencer/unit/import/zendesk/common/article_type_id.rb b/lib/sequencer/unit/import/zendesk/common/article_type_id.rb
index 1b28f34f0..00772d98b 100644
--- a/lib/sequencer/unit/import/zendesk/common/article_type_id.rb
+++ b/lib/sequencer/unit/import/zendesk/common/article_type_id.rb
@@ -23,7 +23,7 @@ class Sequencer
             end
 
             def indirect_map(channel)
-              method_name = "remote_name_#{channel}".to_sym
+              method_name = :"remote_name_#{channel}"
               send(method_name) if respond_to?(method_name, true)
             end
 
diff --git a/lib/sequencer/unit/import/zendesk/sub_sequence/mapped.rb b/lib/sequencer/unit/import/zendesk/sub_sequence/mapped.rb
index 92313b460..331140edd 100644
--- a/lib/sequencer/unit/import/zendesk/sub_sequence/mapped.rb
+++ b/lib/sequencer/unit/import/zendesk/sub_sequence/mapped.rb
@@ -7,7 +7,7 @@ class Sequencer
             module ClassMethods
 
               def resource_map
-                "#{resource_klass.underscore}_map".to_sym
+                :"#{resource_klass.underscore}_map"
               end
 
               def inherited(base)
diff --git a/spec/support/capybara/driven_by.rb b/spec/support/capybara/driven_by.rb
index 18709e8a3..04b681c90 100644
--- a/spec/support/capybara/driven_by.rb
+++ b/spec/support/capybara/driven_by.rb
@@ -14,6 +14,6 @@ RSpec.configure do |config|
 
     # set custom Zammad driver (e.g. zammad_chrome) for special
     # functionalities and CI requirements
-    driven_by("zammad_#{ENV.fetch('BROWSER', 'firefox')}".to_sym)
+    driven_by(:"zammad_#{ENV.fetch('BROWSER', 'firefox')}")
   end
 end
diff --git a/test/unit/email_process_auto_response_test.rb b/test/unit/email_process_auto_response_test.rb
index 9b11ad11b..edd0374e4 100644
--- a/test/unit/email_process_auto_response_test.rb
+++ b/test/unit/email_process_auto_response_test.rb
@@ -57,7 +57,7 @@ Subject: some new subject
 Some Text"
 
     _ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(true, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(true, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
     assert_equal(2, article_p.ticket.articles.count)
 
@@ -69,7 +69,7 @@ X-Loop: yes
 Some Text"
 
     _ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
     assert_equal(1, article_p.ticket.articles.count)
 
@@ -81,7 +81,7 @@ Precedence: Bulk
 Some Text"
 
     _ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
 
     email_raw_string = "From: me@example.com
 To: customer@example.com
@@ -93,7 +93,7 @@ Some Text"
     assert_equal(1, article_p.ticket.articles.count)
 
     _ticket_p, _article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
 
     email_raw_string = "From: me@example.com
 To: customer@example.com
@@ -104,7 +104,7 @@ X-Auto-Response-Suppress: All
 Some Text"
 
     _ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
     assert_equal(1, article_p.ticket.articles.count)
 
@@ -117,7 +117,7 @@ Message-ID: <1234@#{fqdn}>
 Some Text"
 
     _ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
     assert_equal(1, article_p.ticket.articles.count)
 
@@ -130,7 +130,7 @@ Message-ID: <1234@not_matching.#{fqdn}>
 Some Text"
 
     _ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(true, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(true, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
     assert_equal(2, article_p.ticket.articles.count)
 
@@ -180,7 +180,7 @@ Content-Disposition: inline
 test"
 
     _ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
     assert_equal(1, article_p.ticket.articles.count)
 
@@ -221,7 +221,7 @@ X-Loop: yes
 Some Text"
 
     ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
 
     tags = ticket_p.tag_list
@@ -247,7 +247,7 @@ Some Text"
     Setting.set('ticket_trigger_recursive', true)
 
     ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
 
     tags = ticket_p.tag_list
@@ -279,7 +279,7 @@ Subject: some new subject
 Some Text"
 
     ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(true, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(true, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
 
     tags = ticket_p.tag_list
@@ -310,7 +310,7 @@ Some Text"
     Setting.set('ticket_trigger_recursive', true)
 
     ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(true, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(true, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
     tags = ticket_p.tag_list
     assert_equal('new', ticket_p.state.name)
@@ -394,7 +394,7 @@ Subject: some new subject
 Some Text"
 
     _ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(true, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(true, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
     assert_equal(2, article_p.ticket.articles.count)
 
@@ -406,7 +406,7 @@ X-Loop: yes
 Some Text"
 
     _ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
     assert_equal(1, article_p.ticket.articles.count)
 
@@ -418,7 +418,7 @@ Precedence: Bulk
 Some Text"
 
     _ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
 
     email_raw_string = "From: me@example.com
 To: customer@example.com
@@ -430,7 +430,7 @@ Some Text"
     assert_equal(1, article_p.ticket.articles.count)
 
     _ticket_p, _article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
 
     email_raw_string = "From: me@example.com
 To: customer@example.com
@@ -441,7 +441,7 @@ X-Auto-Response-Suppress: All
 Some Text"
 
     _ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
     assert_equal(1, article_p.ticket.articles.count)
 
@@ -454,7 +454,7 @@ Message-ID: <1234@#{fqdn}>
 Some Text"
 
     _ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
     assert_equal(1, article_p.ticket.articles.count)
 
@@ -467,7 +467,7 @@ Message-ID: <1234@not_matching.#{fqdn}>
 Some Text"
 
     _ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(true, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(true, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
     assert_equal(2, article_p.ticket.articles.count)
 
@@ -517,7 +517,7 @@ Content-Disposition: inline
 test"
 
     _ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
     assert_equal(1, article_p.ticket.articles.count)
 
@@ -558,7 +558,7 @@ X-Loop: yes
 Some Text"
 
     ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
 
     tags = ticket_p.tag_list
@@ -584,7 +584,7 @@ Some Text"
     Setting.set('ticket_trigger_recursive', true)
 
     ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
 
     tags = ticket_p.tag_list
@@ -616,7 +616,7 @@ Subject: some new subject
 Some Text"
 
     ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(true, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(true, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
 
     tags = ticket_p.tag_list
@@ -647,7 +647,7 @@ Some Text"
     Setting.set('ticket_trigger_recursive', true)
 
     ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(true, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(true, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
     tags = ticket_p.tag_list
     assert_equal('new', ticket_p.state.name)
@@ -764,7 +764,7 @@ X-Loop: yes
 Some Text"
 
     ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
 
     tags = ticket_p.tag_list
@@ -790,7 +790,7 @@ Some Text"
     Setting.set('ticket_trigger_recursive', true)
 
     ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(false, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(false, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
 
     tags = ticket_p.tag_list
@@ -822,7 +822,7 @@ Subject: some new subject
 Some Text"
 
     ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(true, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(true, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
 
     tags = ticket_p.tag_list
@@ -847,7 +847,7 @@ Some Text"
     Setting.set('ticket_trigger_recursive', true)
 
     ticket_p, article_p, _user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    assert_equal(true, mail['x-zammad-send-auto-response'.to_sym])
+    assert_equal(true, mail[:'x-zammad-send-auto-response'])
     Scheduler.worker(true)
     tags = ticket_p.tag_list
     assert_equal('open', ticket_p.state.name)
diff --git a/test/unit/email_process_reply_to_test.rb b/test/unit/email_process_reply_to_test.rb
index 7213a922a..5e864b244 100644
--- a/test/unit/email_process_reply_to_test.rb
+++ b/test/unit/email_process_reply_to_test.rb
@@ -20,12 +20,12 @@ Some Text"
     assert_equal('marketing_tool@example.com', ticket_p.customer.email)
     assert_equal('Bob', ticket_p.customer.firstname)
     assert_equal('Smith', ticket_p.customer.lastname)
-    assert_nil(mail['raw-origin_from'.to_sym])
-    assert_nil(mail['origin_from'.to_sym])
-    assert_nil(mail['origin_from_email'.to_sym])
-    assert_nil(mail['origin_from_local'.to_sym])
-    assert_nil(mail['origin_from_domain'.to_sym])
-    assert_nil(mail['origin_from_display_name'.to_sym])
+    assert_nil(mail[:'raw-origin_from'])
+    assert_nil(mail[:origin_from])
+    assert_nil(mail[:origin_from_email])
+    assert_nil(mail[:origin_from_local])
+    assert_nil(mail[:origin_from_domain])
+    assert_nil(mail[:origin_from_display_name])
   end
 
   test 'normal processing - take reply to as customer' do
@@ -60,12 +60,12 @@ Some Text"
     assert_equal('replay_to_customer_process2-1@example.com', ticket_p.customer.email)
     assert_equal('Some', ticket_p.customer.firstname)
     assert_equal('Name', ticket_p.customer.lastname)
-    assert_equal('Bob Smith <marketing_tool@example.com>', mail['raw-origin_from'.to_sym].to_s)
-    assert_equal('Bob Smith <marketing_tool@example.com>', mail['origin_from'.to_sym])
-    assert_equal('marketing_tool@example.com', mail['origin_from_email'.to_sym])
-    assert_equal('marketing_tool', mail['origin_from_local'.to_sym])
-    assert_equal('example.com', mail['origin_from_domain'.to_sym])
-    assert_equal('Bob Smith', mail['origin_from_display_name'.to_sym])
+    assert_equal('Bob Smith <marketing_tool@example.com>', mail[:'raw-origin_from'].to_s)
+    assert_equal('Bob Smith <marketing_tool@example.com>', mail[:origin_from])
+    assert_equal('marketing_tool@example.com', mail[:origin_from_email])
+    assert_equal('marketing_tool', mail[:origin_from_local])
+    assert_equal('example.com', mail[:origin_from_domain])
+    assert_equal('Bob Smith', mail[:origin_from_display_name])
   end
 
   test 'normal processing - take reply to as customer and use from as realname' do
@@ -84,12 +84,12 @@ Some Text"
     assert_equal('replay_to_customer_process3@example.com', ticket_p.customer.email)
     assert_equal('Bob', ticket_p.customer.firstname)
     assert_equal('Smith', ticket_p.customer.lastname)
-    assert_equal('Bob Smith <marketing_tool@example.com>', mail['raw-origin_from'.to_sym].to_s)
-    assert_equal('Bob Smith <marketing_tool@example.com>', mail['origin_from'.to_sym])
-    assert_equal('marketing_tool@example.com', mail['origin_from_email'.to_sym])
-    assert_equal('marketing_tool', mail['origin_from_local'.to_sym])
-    assert_equal('example.com', mail['origin_from_domain'.to_sym])
-    assert_equal('Bob Smith', mail['origin_from_display_name'.to_sym])
+    assert_equal('Bob Smith <marketing_tool@example.com>', mail[:'raw-origin_from'].to_s)
+    assert_equal('Bob Smith <marketing_tool@example.com>', mail[:origin_from])
+    assert_equal('marketing_tool@example.com', mail[:origin_from_email])
+    assert_equal('marketing_tool', mail[:origin_from_local])
+    assert_equal('example.com', mail[:origin_from_domain])
+    assert_equal('Bob Smith', mail[:origin_from_display_name])
 
     email = "From: Bob Smith <marketing_tool@example.com>
 To: zammad@example.com
@@ -106,12 +106,12 @@ Some Text"
     assert_equal('replay_to_customer_process3-1@example.com', ticket_p.customer.email)
     assert_equal('Bob', ticket_p.customer.firstname)
     assert_equal('Smith', ticket_p.customer.lastname)
-    assert_equal('Bob Smith <marketing_tool@example.com>', mail['raw-origin_from'.to_sym].to_s)
-    assert_equal('Bob Smith <marketing_tool@example.com>', mail['origin_from'.to_sym])
-    assert_equal('marketing_tool@example.com', mail['origin_from_email'.to_sym])
-    assert_equal('marketing_tool', mail['origin_from_local'.to_sym])
-    assert_equal('example.com', mail['origin_from_domain'.to_sym])
-    assert_equal('Bob Smith', mail['origin_from_display_name'.to_sym])
+    assert_equal('Bob Smith <marketing_tool@example.com>', mail[:'raw-origin_from'].to_s)
+    assert_equal('Bob Smith <marketing_tool@example.com>', mail[:origin_from])
+    assert_equal('marketing_tool@example.com', mail[:origin_from_email])
+    assert_equal('marketing_tool', mail[:origin_from_local])
+    assert_equal('example.com', mail[:origin_from_domain])
+    assert_equal('Bob Smith', mail[:origin_from_display_name])
   end
 
   test 'normal processing - take reply to as customer and sender is system address' do
@@ -141,12 +141,12 @@ Some Text"
     assert_equal('replay_to_customer_process2@example.com', ticket_p.customer.email)
     assert_equal('', ticket_p.customer.firstname)
     assert_equal('', ticket_p.customer.lastname)
-    assert_equal('Marketing Tool <marketing_tool@example.com>', mail['raw-origin_from'.to_sym].to_s)
-    assert_equal('Marketing Tool <marketing_tool@example.com>', mail['origin_from'.to_sym])
-    assert_equal('marketing_tool@example.com', mail['origin_from_email'.to_sym])
-    assert_equal('marketing_tool', mail['origin_from_local'.to_sym])
-    assert_equal('example.com', mail['origin_from_domain'.to_sym])
-    assert_equal('Marketing Tool', mail['origin_from_display_name'.to_sym])
+    assert_equal('Marketing Tool <marketing_tool@example.com>', mail[:'raw-origin_from'].to_s)
+    assert_equal('Marketing Tool <marketing_tool@example.com>', mail[:origin_from])
+    assert_equal('marketing_tool@example.com', mail[:origin_from_email])
+    assert_equal('marketing_tool', mail[:origin_from_local])
+    assert_equal('example.com', mail[:origin_from_domain])
+    assert_equal('Marketing Tool', mail[:origin_from_display_name])
   end
 
 end