Postfix errors sending and such

[kilburn]

Is the user authenticated when trying to send the mail (look in /var/log/mail.log)? I think you disabled authentication when not using TLS, so now that you disabled it your users are unable to authenticate and thus their mails to external domains are rejected.

If it's not the case or you want further information, please post the relevant mail.log lines corresponding to a delivery attempt (from the "connect" one to "disconnect").