Duplicate header MIME-Version when using Amazon SES as mail relay

[DANgerous25]

Hi all, my ISP blocks outbound SMTP so I'm trying to get my SL self-host working with SES. I've followed this guide for your reference.

I've now got to a point where the first email to verify a new user is getting bounced. The bounce message (which I presume comes from SES) looks like this from my postfix log /var/log/mail.log:

Sep 21 21:06:22 myserver postfix/smtp[494856]: 950083806B3: to=<[email protected]>, relay=email-smtp.ap-northeast-1.amazonaws.com[18.176.73.83]:587, delay=1.5, delays=0.27/0.08/0.71/0.43, dsn=5.0.0, status=bounced (host email-smtp.ap-northeast-1.amazonaws.com[18.176.73.83] said: 554 Transaction failed: Duplicate header 'MIME-Version'. (in reply to end of DATA command))

Internet searches yield many many cases of folks with similar issues when they switch to SES. In almost all cases I can find, the suggested solution is for apps to fix their code not to provide duplicate headers.

Looking at my email logs for the sl-email container I get this:

2022-09-21 13:06:22,870 - SL - DEBUG - 1 - "email_handler.py:2010" - handle() - 0c633a4a-ac19-4a50-894a-0aede567583c - Cannot parse Postfix queue ID from ['by simple.mysldomain.com (Postfix)\r\n\tid D00943806B5; Wed, 21 Sep 2022 21:06:22 +0800 (HKT)'] by simple.mysldomain.com (Postfix)
	id D00943806B5; Wed, 21 Sep 2022 21:06:22 +0800 (HKT)
2022-09-21 13:06:23,013 - SL - DEBUG - 1 - "email_handler.py:2036" - handle() - 0c633a4a-ac19-4a50-894a-0aede567583c - ==>> Handle mail_from:<>, rcpt_tos:['[email protected]'], header_from:[email protected] (Mail Delivery System), header_to:[email protected], cc:None, reply-to:None, message_id:<[email protected]>, client_ip:None, headers:[('Received', 'by simple.mysldomain.com (Postfix)\r\n\tid D00943806B5; Wed, 21 Sep 2022 21:06:22 +0800 (HKT)'), ('Date', 'Wed, 21 Sep 2022 21:06:22 +0800 (HKT)'), ('From', '[email protected] (Mail Delivery System)'), ('Subject', 'Undelivered Mail Returned to Sender'), ('To', '[email protected]'), ('Auto-Submitted', 'auto-replied'), ('MIME-Version', '1.0'), ('Content-Type', 'multipart/report; report-type=delivery-status;\r\n\tboundary="950083806B3.1663765582/simple.mysldomain.com"'), ('Content-Transfer-Encoding', '8bit'), ('Message-Id', '<[email protected]>')], mail_options:['SIZE=24813', 'BODY=8BITMIME'], rcpt_options:[]
2022-09-21 13:06:23,019 - SL - DEBUG - 1 - "email_handler.py:1880" - handle_transactional_bounce() - 0c633a4a-ac19-4a50-894a-0aede567583c - handle transactional bounce sent to [email protected]
2022-09-21 13:06:23,021 - SL - INFO - 1 - "email_handler.py:1888" - handle_transactional_bounce() - 0c633a4a-ac19-4a50-894a-0aede567583c - Create bounce for [email protected]
2022-09-21 13:06:23,021 - SL - WARNING - 1 - "/code/app/email_utils.py:697" - get_mailbox_bounce_info() - 0c633a4a-ac19-4a50-894a-0aede567583c - add missing content-transfer-encoding header
2022-09-21 13:06:23,031 - SL - INFO - 1 - "email_handler.py:2414" - _handle() - 0c633a4a-ac19-4a50-894a-0aede567583c - Finish mail_from <>, rcpt_tos ['[email protected]'], takes 0.16266489028930664 seconds with return code '250 SL E205 bounce handled'<<===mysldomain.com

Unfortunately I have no clue how to debug this, or how to work around or fix the issue. Hopefully someone can help?

N.B. in changing what I thought to be personal information in the two snippets above, I lost consistency but I hope that's not important in the context of the question.

[DANgerous25]

With hints from this article I've managed to get a workaround working:

1. create a file /etc/postfix/header_checks

echo '/^Mime-Version:/ IGNORE' > /etc/postfix/header_checks

2. Update postfix main.cf

postconf -e "header_checks = regexp:/etc/postfix/header_checks"

3. restart postfix and put your feet up

I don't know the implications of doing this but it appears to work. I'm all ears if anyone has any insight!

[nguyenkims]

@DANgerous25 this is indeed a bug in SimpleLogin, the fix is in #1302 and I'll try to prepare a new self-hosting version when the fix is merged.

[DANgerous25]

Fantastic. Is there any downside to my workaround in the meantime?

[nguyenkims]

I'm not familiar with /etc/postfix/header_checks syntax so not sure what it's doing unfortunately.