fix: Improve mail content parsing (#2638)

app/mailboxes/support_mailbox.rb

@@ -9,11 +9,13 @@ class SupportMailbox < ApplicationMailbox
                     :decorate_mail
 
   def process
+    ActiveRecord::Base.transaction do
       find_or_create_contact
       create_conversation
       create_message
       add_attachments_to_message
     end
+  end
 
   private
 

app/presenters/mail_presenter.rb

@@ -12,7 +12,7 @@ class MailPresenter < SimpleDelegator
   end
 
   def text_content
-    @decoded_text_content ||= encode_to_unicode(text_part&.decoded || mail.decoded || '')
+    @decoded_text_content ||= encode_to_unicode(text_part&.decoded || decoded_message || '')
 
     return {} if @decoded_text_content.blank?
 
@@ -47,6 +47,14 @@ class MailPresenter < SimpleDelegator
     end
   end
 
+  def decoded_message
+    if mail.multipart?
+      return mail.text_part ? mail.text_part.decoded : nil
+    end
+
+    mail.decoded
+  end
+
   def number_of_attachments
     mail.attachments.count
   end