No, I’m not using SendGrid – this Discourse installation is several years old, and at the time I wrote an AWS Lambda that used the /admin/email/handle_mail API to push incoming mail into Discourse. That Lambda script used Python 2.7, so it is due for a rewrite…probably time to see what my options are now.
Oddly, the “We detected an outdated version of mail-receiver…” is no longer on my Discourse admin dashboard. Huh. Scratch that – the message is still there. Maybe it went away because the Discourse install didn’t receive any inbound messages for a few days on the /admin/email/handle_mail endpoint, but it did when I sent the test message?
Just checked – inbound mail to Discourse still works.