We use Service Desk feature of Gitlab to track support issues - you send an email to create gitlab issues (you don’t need an account). But currently it will reject emails with an empty subject. Ideally this should be fixed in gitlab, but this issue was reported in 2021 with no fix yet Service desk rejected email (#330309) · Issues · GitLab.org / GitLab · GitLab
So as a work around, we are considering to route service desk emails via mailman (which can also keep an archive of original emails). Based on our initial tests, we have modified SPF and rspamd settings to allow forwarded mails to be accepted by mailman. More testing from different email providers would be welcome. We already tested, riseup, proton, gmail, icloud, posteo, autistici and zoho mail. If you can help with this test (especially mail.com, yahoo and microsoft), send an email to test-service-desk at puri.sm and comment here if you received an acknowledgment mail and mention your email provider.
We have now switched all our service desks to pass mails via mailman to support empty subjects in support mails. If you have mail.com, yahoo or microsoft accounts, a confirmation about email delivery would still be appreciated (7 email providers were successfully tested so far).