I recently got a new MacBook Pro, and as I was setting up the mail configuration on that laptop, I found that I was unable to send mail through my mail server. I use Apple Mail, and usually it works great for me, but in this case it was not working with my Postfix server.
I made several attempts at fixing this issue, but I always got the same error:
postfix/submission/smtpd: NOQUEUE: reject: RCPT from REDACTED[X.X.X.X]: 554 5.7.1 <firstname.lastname@example.org>: Recipient address rejected: Access denied; from=<email@example.com> to=<firstname.lastname@example.org> proto=ESMTP helo=<[REDACTED]>
After exhausting everything I could think of, and after much troubleshooting, I determined that all settings were correct: other systems could send mail through my Postfix server, but I still had the problem with the new laptop.
At one point I had the idea to disable Apple Mail's SMTP server checkbox that sets the application to "Automatically manage connection settings," so I did that and I confirmed the settings that it had been automatically managing -- the port and TLS/SSL setting (587/SSL) and authentication configuration.
Once I disabled the automatic option, everything worked correctly. I didn't actually change any configuration, and all of the settings were correct, it just doesn't work automatically.
I post this that others might find it useful, and that I might find it when I set up my next system.