Support for ARC

[Mygod]

Can we please support the ARC protocol? It will reduce the likelihood that the forwarded email goes into spam.

https://support.google.com/a/answer/13198639?sjid=16402237990595946972-NA
https://datatracker.ietf.org/doc/rfc8617/

[huan]

I’d love to review a PR for that!

[Mygod]

For example, if the source domain does not have a DKIM record but has a SPF record, the mail will not go through.

postfix/smtp[12529]: EF7A17EBEE: to=<[email protected]>, orig_to=<[email protected]>, relay=gmail-smtp-in.l.google.com[74.125.142.27]:25, delay=3.4, delays=2.9/0/0.1/0.45, dsn=5.7.26, status=bounced (host gmail-smtp-in.l.google.com[74.125.142.27] said: 550-5.7.26 The MAIL FROM domain [source.domain] has an SPF record with a 550-5.7.26 hard fail policy (-all) but it fails to pass SPF checks with the ip: 550-5.7.26 [docker.ip]. To best protect our users from spam and phishing, 550-5.7.26 the message has been blocked. Please visit 550-5.7.26 https://support.google.com/mail/answer/81126#authentication for more 550 5.7.26 information. - gsmtp (in reply to end of DATA command))

[Mygod]

Also the bounced email generated sending back to source email does not appear to use DKIM authentication itself either, causing further DKIM failures.