New comment by sdgathman on void-packages repository

https://github.com/void-linux/void-packages/issues/39918#issuecomment-1303743103

Comment:
Date fields, including Received header, SHOULD use local time expressed as offset from UTC (not TZ abbreviation).  https://www.rfc-editor.org/rfc/rfc2822#section-3.3

If localtime is UTC, they SHOULD use +0000.  If defaulting to UTC because localtime is unknown - they SHOULD use -0000.

Your example uses +0000.  Also, your log example uses the same TZ from the logging system and from opensmtpd - suggesting that they both use the same config.  That sounds to me like you have the system configured to UTC, and have only configured a personal preference somewhere as CEST.