Steps to Reproduce

1. Configure a Mail Handler
2. Try creating a ticket via email with file of about 8Mb attached to the mail

Expected Results

The issue is successfully created and the file is attached to the mail.

Actual Results

The issue creation fails.

Return mail reports:

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain instance.atlassian.net by mx-103.ash2.uc-inf.net. [xxx.xxx.xxx.xxx].

The error that the other server returned was:
552 5.3.4 Message size exceeds fixed limit

Notes

Increasing the attachment size limit doesn't fix the issue

Workaround

None so far.