diff --git a/app/models/channel/driver/imap.rb b/app/models/channel/driver/imap.rb
index 474afb1a1..090dd9ee5 100644
--- a/app/models/channel/driver/imap.rb
+++ b/app/models/channel/driver/imap.rb
@@ -160,11 +160,11 @@ example
 
         message_meta = nil
         timeout(1.minute) do
-          message_meta = @imap.fetch(message_id, ['RFC822.HEADER'])[0].attr
+          message_meta = @imap.fetch(message_id, ['RFC822.HEADER'])[0]
         end
 
         # check how many content messages we have, for notice used
-        headers = parse_headers(message_meta['RFC822.HEADER'])
+        headers = self.class.extract_rfc822_headers(message_meta)
         next if messages_is_verify_message?(headers)
         next if messages_is_ignore_message?(headers)
 
@@ -191,11 +191,12 @@ example
 
         message_meta = nil
         timeout(FETCH_METADATA_TIMEOUT) do
-          message_meta = @imap.fetch(message_id, ['ENVELOPE'])[0].attr
+          message_meta = @imap.fetch(message_id, ['RFC822.HEADER'])[0]
         end
 
         # check if verify message exists
-        subject = message_meta['ENVELOPE'].subject
+        headers = self.class.extract_rfc822_headers(message_meta)
+        subject = headers['Subject']
         next if !subject
         next if !subject.match?(/#{verify_string}/)
 
@@ -237,7 +238,7 @@ example
 
       message_meta = nil
       timeout(FETCH_METADATA_TIMEOUT) do
-        message_meta = @imap.fetch(message_id, ['RFC822.SIZE', 'ENVELOPE', 'FLAGS', 'INTERNALDATE', 'RFC822.HEADER'])[0]
+        message_meta = @imap.fetch(message_id, ['RFC822.SIZE', 'FLAGS', 'INTERNALDATE', 'RFC822.HEADER'])[0]
       rescue Net::IMAP::ResponseParseError => e
         raise if !e.message.include?('unknown token')
 
@@ -357,10 +358,35 @@ returns
     false
   end
 
+  # Parses RFC822 header
+  # @param [String] RFC822 header text blob
+  # @return [Hash<String=>String>]
+  def self.parse_rfc822_headers(string)
+    array = string
+              .gsub("\r\n\t", ' ') # Some servers (e.g. office365) may put attribute value on a separate line and tab it
+              .lines(chomp: true)
+              .map { |line| line.split(/:\s*/, 2).map(&:strip) }
+
+    array.each { |elem| elem.append(nil) if elem.one? }
+
+    Hash[*array.flatten]
+  end
+
+  # Parses RFC822 header
+  # @param [Net::IMAP::FetchData] fetched message
+  # @return [Hash<String=>String>]
+  def self.extract_rfc822_headers(message_meta)
+    blob = message_meta&.attr&.dig 'RFC822.HEADER'
+
+    return unless blob
+
+    parse_rfc822_headers blob
+  end
+
   private
 
   def messages_is_too_old_verify?(message_meta, count, count_all)
-    headers = parse_headers(message_meta.attr['RFC822.HEADER'])
+    headers = self.class.extract_rfc822_headers(message_meta)
     return true if !messages_is_verify_message?(headers)
     return true if headers['X-Zammad-Verify-Time'].blank?
 
@@ -389,20 +415,6 @@ returns
     false
   end
 
-  def parse_headers(string)
-    return {} if string.blank?
-
-    headers = {}
-    headers_pairs = string.split("\r\n")
-    headers_pairs.each do |pair|
-      key_value = pair.split(': ')
-      next if key_value[0].blank?
-
-      headers[key_value[0]] = key_value[1]
-    end
-    headers
-  end
-
 =begin
 
 check if email is already impoted
@@ -419,10 +431,11 @@ returns
   def already_imported?(message_id, message_meta, count, count_all, keep_on_server, channel)
     # rubocop:enable Metrics/ParameterLists
     return false if !keep_on_server
-    return false if !message_meta.attr
-    return false if !message_meta.attr['ENVELOPE']
 
-    local_message_id = message_meta.attr['ENVELOPE'].message_id
+    headers = self.class.extract_rfc822_headers(message_meta)
+    retrurn false if !headers
+
+    local_message_id = headers['Message-ID']
     return false if local_message_id.blank?
 
     local_message_id_md5 = Digest::MD5.hexdigest(local_message_id)
diff --git a/spec/models/channel/driver/imap_spec.rb b/spec/models/channel/driver/imap_spec.rb
index 8d8b20791..b080ae542 100644
--- a/spec/models/channel/driver/imap_spec.rb
+++ b/spec/models/channel/driver/imap_spec.rb
@@ -23,4 +23,51 @@ RSpec.describe Channel::Driver::Imap do
       expect(result.dig(:result)).to eq 'ok'
     end
   end
+
+  describe '.parse_rfc822_headers' do
+    it 'parses simple header' do
+      expect(described_class.parse_rfc822_headers('Key: Value')).to have_key('Key').and(have_value('Value'))
+    end
+
+    it 'parses header with no white space' do
+      expect(described_class.parse_rfc822_headers('Key:Value')).to have_key('Key').and(have_value('Value'))
+    end
+
+    it 'parses multiline header' do
+      expect(described_class.parse_rfc822_headers("Key: Value\r\n2nd-key: 2nd-value"))
+        .to have_key('Key').and(have_value('Value')).and(have_key('2nd-key')).and(have_value('2nd-value'))
+    end
+
+    it 'parses value with semicolons' do
+      expect(described_class.parse_rfc822_headers('Key: Val:ue')).to have_key('Key').and(have_value('Val:ue'))
+    end
+
+    it 'parses key-only lines' do
+      expect(described_class.parse_rfc822_headers('Key')).to have_key('Key')
+    end
+
+    it 'handles empty line' do
+      expect { described_class.parse_rfc822_headers("Key: Value\r\n") }.not_to raise_error
+    end
+
+    it 'handles tabbed value' do
+      expect(described_class.parse_rfc822_headers("Key: \r\n\tValue")).to have_key('Key').and(have_value('Value'))
+    end
+  end
+
+  describe '.extract_rfc822_headers' do
+    it 'extracts header' do
+      object = Net::IMAP::FetchData.new :id, { 'RFC822.HEADER' => 'Key: Value' }
+      expect(described_class.extract_rfc822_headers(object)).to have_key('Key').and(have_value('Value'))
+    end
+
+    it 'returns nil when header attribute is missing' do
+      object = Net::IMAP::FetchData.new :id, { 'Another' => 'Key: Value' }
+      expect(described_class.extract_rfc822_headers(object)).to be_nil
+    end
+
+    it 'does not raise error when given nil' do
+      expect { described_class.extract_rfc822_headers(nil) }.not_to raise_error
+    end
+  end
 end