fix: Raise error if email to_header is invalid (#8688)

app/mailboxes/application_mailbox.rb

@@ -37,10 +37,24 @@ class ApplicationMailbox < ActionMailbox::Base
     # checks if follow this pattern  send it to reply_mailbox
     # reply+<conversation-uuid>@<mailer-domain.com>
     def reply_uuid_mail?(inbound_mail)
+      validate_to_address(inbound_mail)
+
       inbound_mail.mail.to&.any? do |email|
         conversation_uuid = email.split('@')[0]
         conversation_uuid.match?(REPLY_EMAIL_UUID_PATTERN)
       end
     end
+
+    # if mail.to returns a string, then it is a malformed `to` header
+    # valid `to` header will be of type Mail::AddressContainer
+    # validate if the to address is of type string
+    def validate_to_address(inbound_mail)
+      to_address_class = inbound_mail.mail.to&.class
+
+      return if to_address_class == Mail::AddressContainer
+
+      Rails.logger.error "Email to address header is malformed `#{inbound_mail.mail.to}`"
+      raise StandardError, "Invalid email to address header #{inbound_mail.mail.to}"
+    end
   end
 end