Configure direct-delivery incoming email for self-hosted sites with Mail-Receiver

As far as I can tell my set up is right, but there’s no record of any of the emails in Discourse.

The emails show up in the log like this:

Mar 18 17:20:41 [myserver]-mail-receiver postfix/smtpd[122]: NOQUEUE: reject: RCPT from [XXX][XXX.XX.XXX.XXX]: 554 5.7.1 <test004@www.[mysite].com>: Recipient address rejected: Mail to this address is not accepted. Check the address and try to send again?; from=<[sender]> to=<test004@www.[mysite].com> proto=ESMTP helo=<[XXX]>
Mar 18 17:20:42 [myserver]-mail-receiver postfix/smtpd[122]: disconnect from [XXX][XXX.XX.XXX.XXX] ehlo=2 starttls=1 mail=1 rcpt=0/1 bdat=0/1 quit=1 commands=5/7

And I get a rejection notification at the sending address as well. Nothing remains in the queue and there aren’t any trace errors in the logs. I triple checked that the URLs all match, and the API settings page shows that the key is being used. But the rejected email list in the admin panel stays empty.

Any suggestions?