[Bug]: Email Bogus MIME version and other deliverability issues

[brandonkal]

Preflight Checklist

• I could not find a solution in the documentation, the existing issues or discussions
• I have joined the ZITADEL chat

Environment

ZITADEL Cloud

Version

Latest

Database

None

Database Version

No response

Describe the problem caused by this bug

mail-tester.com is reporting a Bogus MIME version header from the initial user email. I assume this is the same issue with the other transactional emails.

Other issues to improve deliverability:

1. No text/plain version. This should be easy to fix.
2. HTML version has font has low contrast

To reproduce

1. Go to mail-tester.com and copy the email address
2. Register a new user using this address
3. Check the deliverability score

Screenshots

Expected behavior

No response

Operating System

No response

Relevant Configuration

No response

Additional Context

No response

[stebenz]

Hi @brandonkal

Not quite sure, I tried to find out if this is a case of case-sensitivity where there is no defined handling.
Created #7886 for the version.

With the definition under RFC-2045 it should be "MIME-Version", but with RFC-2045 Section 2:

 All numeric and octet values are given in decimal notation in this
 set of documents. All media type values, subtype values, and
 parameter names as defined are case-insensitive.  However, parameter
 values are case-sensitive unless otherwise specified for the specific
 parameter.

and "parameter names as defined are case-insesitive", I'm not sure if mail-tester.com maybe handles it wrong, do you have any information about that?

[brandonkal]

Mail-tester is using SpamAssassin for that score. So I would think it is handling it correctly since SpamAssassin is commonly deployed

[stebenz]

@brandonkal we deployed a fix with v2.51.1 for the bogus MIME version, could you please check and then we can close this issue?