diff --git a/Gemfile b/Gemfile
index 447dd2303..cc24e5572 100644
--- a/Gemfile
+++ b/Gemfile
@@ -164,8 +164,9 @@ group :development, :test do
   # changelog generation
   gem 'github_changelog_generator'
 
-  # Use Factory Bot for generating random test data
+  # generate random test data
   gem 'factory_bot_rails'
+  gem 'faker'
 
   # mock http calls
   gem 'webmock'
diff --git a/Gemfile.lock b/Gemfile.lock
index c7ff844a4..b850f3494 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -165,6 +165,8 @@ GEM
     factory_bot_rails (4.8.2)
       factory_bot (~> 4.8.2)
       railties (>= 3.0.0)
+    faker (1.9.1)
+      i18n (>= 0.7)
     faraday (0.12.2)
       multipart-post (>= 1.2, < 3)
     faraday-http-cache (2.0.0)
@@ -533,6 +535,7 @@ DEPENDENCIES
   eventmachine
   execjs
   factory_bot_rails
+  faker
   github_changelog_generator
   guard
   guard-livereload
diff --git a/spec/models/channel/email_parser_spec.rb b/spec/models/channel/email_parser_spec.rb
index 512efc858..80562efda 100644
--- a/spec/models/channel/email_parser_spec.rb
+++ b/spec/models/channel/email_parser_spec.rb
@@ -1,103 +1,141 @@
 require 'rails_helper'
 
 RSpec.describe Channel::EmailParser, type: :model do
+  let(:subject)   { described_class.new }
   let(:mail_file) { Rails.root.join('test', 'data', 'mail', 'mail001.box') }
-  let(:raw_mail) { File.read(mail_file) }
+  let(:raw_mail)  { File.read(mail_file) }
 
   describe '#process' do
-    let(:raw_mail) { File.read(mail_file).sub(/(?<=^Subject: ).*$/, test_string) }
-    let(:test_string) do
-      Setting.get('ticket_hook') + Setting.get('ticket_hook_divider') + ticket.number
-    end
-    let(:ticket) { create(:ticket) }
+    let(:raw_mail)    { File.read(mail_file).sub(/(?<=^Subject: ).*$/, test_string) }
+    let(:test_string) { Setting.get('ticket_hook') + Setting.get('ticket_hook_divider') + ticket.number }
+    let(:ticket)      { create(:ticket) }
 
-    context 'when email subject contains ticket reference' do
-      it 'adds message to ticket' do
-        expect { described_class.new.process({}, raw_mail) }
-          .to change { ticket.articles.length }
+    context 'for creating new users' do
+      context 'with one unrecognized email address' do
+        let(:raw_mail) { <<~RAW }
+          From: #{Faker::Internet.unique.email}
+          To: #{User.pluck(:email).reject(&:blank?).sample}
+          Subject: Foo bar
+
+          Lorem ipsum dolor
+        RAW
+
+        it 'creates one new user' do
+          expect { Channel::EmailParser.new.process({}, raw_mail) }
+            .to change { User.count }.by(1)
+        end
+      end
+
+      context 'with a large number (42+) of unrecognized email addresses' do
+        let(:raw_mail) { <<~RAW }
+          From: #{Faker::Internet.unique.email}
+          To: #{Array.new(22) { Faker::Internet.unique.email }.join(', ')}
+          Cc: #{Array.new(22) { Faker::Internet.unique.email }.join(', ')}
+          Subject: test max sender identify
+
+          Some Text
+        RAW
+
+        it 'never creates more than 41 users per email' do
+          expect { Channel::EmailParser.new.process({}, raw_mail) }
+            .to change { User.count }.by(41)
+        end
       end
     end
 
-    context 'when configured to search body' do
-      before { Setting.set('postmaster_follow_up_search_in', 'body') }
-
-      context 'when body contains ticket reference' do
-        context 'in visible text' do
-          let(:raw_mail) { File.read(mail_file).sub(/Hallo =\nMartin,(?=<o:p>)/, test_string) }
-
-          it 'adds message to ticket' do
-            expect { described_class.new.process({}, raw_mail) }
-              .to change { ticket.articles.length }
-          end
+    context 'for associating emails to tickets' do
+      context 'when email subject contains ticket reference' do
+        it 'adds message to ticket' do
+          expect { described_class.new.process({}, raw_mail) }
+            .to change { ticket.articles.length }
         end
+      end
 
-        context 'as part of a larger word' do
-          let(:raw_mail) { File.read(mail_file).sub(/(?<=Hallo) =\n(?=Martin,<o:p>)/, test_string) }
+      context 'when configured to search body' do
+        before { Setting.set('postmaster_follow_up_search_in', 'body') }
 
-          it 'creates a separate ticket' do
-            expect { described_class.new.process({}, raw_mail) }
-              .not_to change { ticket.articles.length }
+        context 'when body contains ticket reference' do
+          context 'in visible text' do
+            let(:raw_mail) { File.read(mail_file).sub(/Hallo =\nMartin,(?=<o:p>)/, test_string) }
+
+            it 'adds message to ticket' do
+              expect { described_class.new.process({}, raw_mail) }
+                .to change { ticket.articles.length }
+            end
           end
-        end
 
-        context 'in html attributes' do
-          let(:raw_mail) { File.read(mail_file).sub(%r{<a href.*?/a>}m, %(<table bgcolor="#{test_string}"> </table>)) }
+          context 'as part of a larger word' do
+            let(:raw_mail) { File.read(mail_file).sub(/(?<=Hallo) =\n(?=Martin,<o:p>)/, test_string) }
 
-          it 'creates a separate ticket' do
-            expect { described_class.new.process({}, raw_mail) }
-              .not_to change { ticket.articles.length }
+            it 'creates a separate ticket' do
+              expect { described_class.new.process({}, raw_mail) }
+                .not_to change { ticket.articles.length }
+            end
+          end
+
+          context 'in html attributes' do
+            let(:raw_mail) { File.read(mail_file).sub(%r{<a href.*?/a>}m, %(<table bgcolor="#{test_string}"> </table>)) }
+
+            it 'creates a separate ticket' do
+              expect { described_class.new.process({}, raw_mail) }
+                .not_to change { ticket.articles.length }
+            end
           end
         end
       end
     end
 
-    # see https://github.com/zammad/zammad/issues/2198
-    context 'when sender address contains spaces (#2198)' do
-      let(:mail_file) { Rails.root.join('test', 'data', 'mail', 'mail071.box') }
-      let(:sender_email) { 'powerquadrantsystem@example.com' }
+    context 'for sender/recipient address formatting' do
+      # see https://github.com/zammad/zammad/issues/2198
+      context 'when sender address contains spaces (#2198)' do
+        let(:mail_file) { Rails.root.join('test', 'data', 'mail', 'mail071.box') }
+        let(:sender_email) { 'powerquadrantsystem@example.com' }
 
-      it 'removes them before creating a new user' do
-        expect { described_class.new.process({}, raw_mail) }
-          .to change { User.where(email: sender_email).count }.to(1)
+        it 'removes them before creating a new user' do
+          expect { described_class.new.process({}, raw_mail) }
+            .to change { User.where(email: sender_email).count }.to(1)
+        end
+
+        it 'marks new user email as invalid' do
+          described_class.new.process({}, raw_mail)
+
+          expect(User.find_by(email: sender_email).preferences)
+            .to include('mail_delivery_failed' => true)
+            .and include('mail_delivery_failed_reason' => 'invalid email')
+            .and include('mail_delivery_failed_data' => a_kind_of(ActiveSupport::TimeWithZone))
+        end
       end
 
-      it 'marks new user email as invalid' do
-        described_class.new.process({}, raw_mail)
+      # see https://github.com/zammad/zammad/issues/2254
+      context 'when sender address contains > (#2254)' do
+        let(:mail_file) { Rails.root.join('test', 'data', 'mail', 'mail076.box') }
+        let(:sender_email) { 'millionslotteryspaintransfer@example.com' }
 
-        expect(User.find_by(email: sender_email).preferences)
-          .to include('mail_delivery_failed' => true)
-          .and include('mail_delivery_failed_reason' => 'invalid email')
-          .and include('mail_delivery_failed_data' => a_kind_of(ActiveSupport::TimeWithZone))
+        it 'removes them before creating a new user' do
+          expect { described_class.new.process({}, raw_mail) }
+            .to change { User.where(email: sender_email).count }.to(1)
+        end
+
+        it 'marks new user email as invalid' do
+          described_class.new.process({}, raw_mail)
+
+          expect(User.find_by(email: sender_email).preferences)
+            .to include('mail_delivery_failed' => true)
+            .and include('mail_delivery_failed_reason' => 'invalid email')
+            .and include('mail_delivery_failed_data' => a_kind_of(ActiveSupport::TimeWithZone))
+        end
       end
     end
 
-    # see https://github.com/zammad/zammad/issues/2254
-    context 'when sender address contains > (#2254)' do
-      let(:mail_file) { Rails.root.join('test', 'data', 'mail', 'mail076.box') }
-      let(:sender_email) { 'millionslotteryspaintransfer@example.com' }
+    context 'for charset handling' do
+      # see https://github.com/zammad/zammad/issues/2224
+      context 'when header specifies Windows-1258 charset (#2224)' do
+        let(:mail_file) { Rails.root.join('test', 'data', 'mail', 'mail072.box') }
 
-      it 'removes them before creating a new user' do
-        expect { described_class.new.process({}, raw_mail) }
-          .to change { User.where(email: sender_email).count }.to(1)
-      end
-
-      it 'marks new user email as invalid' do
-        described_class.new.process({}, raw_mail)
-
-        expect(User.find_by(email: sender_email).preferences)
-          .to include('mail_delivery_failed' => true)
-          .and include('mail_delivery_failed_reason' => 'invalid email')
-          .and include('mail_delivery_failed_data' => a_kind_of(ActiveSupport::TimeWithZone))
-      end
-    end
-
-    # see https://github.com/zammad/zammad/issues/2224
-    context 'when header specifies Windows-1258 charset (#2224)' do
-      let(:mail_file) { Rails.root.join('test', 'data', 'mail', 'mail072.box') }
-
-      it 'does not raise Encoding::ConverterNotFoundError' do
-        expect { described_class.new.process({}, raw_mail) }
-          .not_to raise_error
+        it 'does not raise Encoding::ConverterNotFoundError' do
+          expect { described_class.new.process({}, raw_mail) }
+            .not_to raise_error
+        end
       end
     end
   end
diff --git a/spec/support/faker.rb b/spec/support/faker.rb
new file mode 100644
index 000000000..00d3734f6
--- /dev/null
+++ b/spec/support/faker.rb
@@ -0,0 +1,5 @@
+RSpec.configure do |config|
+  config.after(:each) do
+    Faker::UniqueGenerator.clear
+  end
+end
diff --git a/test/unit/email_process_identify_sender_max_test.rb b/test/unit/email_process_identify_sender_max_test.rb
deleted file mode 100644
index ee7ffe0b0..000000000
--- a/test/unit/email_process_identify_sender_max_test.rb
+++ /dev/null
@@ -1,25 +0,0 @@
-require 'test_helper'
-
-class EmailProcessIdentifySenderMax < ActiveSupport::TestCase
-
-  test 'text max created recipients per email' do
-    current_users = User.count
-    email_raw_string = "From: #{generate_recipient}
-To: #{generate_recipient(22)}
-Cc: #{generate_recipient(22)}
-Subject: test max sender identify
-
-Some Text"
-
-    ticket_p, article_p, user_p, mail = Channel::EmailParser.new.process({}, email_raw_string)
-    ticket = Ticket.find(ticket_p.id)
-    assert_equal('test max sender identify', ticket.title)
-    assert_equal(current_users + 41, User.count)
-  end
-
-  def generate_recipient(count = 1)
-    uid = -> { rand(999_999_999_999_999) }
-    Array.new(count) { "#{uid.call}@#{uid.call}.example.com" }.join(', ')
-  end
-
-end