Created attachment 435074 [details, diff] patch fixing the issue Currently, mime-construct does not include "Date" field in generated messages. This field is required according to RFC 5322 and not every MTA or SMTP client adds it when it is missing (for example mail-mta/msmtp doesn't). This means that mail clients often timestamp such messages as either 01.01.1970 or date it was first seen by them rather than posting date. A possible fix is to use Email::Date::Format to easily format "Date" field value. I attach a simple patch to do it. This would also require adding dev-perl/Email-Date-Format to dev-perl/mime-construct runtime dependencies. I've added this as CPAN bug 111372 a few months ago and mailed mime-construct author about it but there was no response - the software had last release in 2010 so it is probably no longer maintained.
Created Github PR 3408 that resolves this issue.
Closing this bug since the PR was merged.