I'm a developer for an online web service. A supplemental component of our main product is a feature whereby users can forward emails to us and have them automagically imported to the appropriate spot in their account. Recently, we've started noticing a handful of email rejections, almost always from one (legitimate) mail server. The following is a recent error from our postfix logs:
Dec 2 15:43:57 ffck47ab.joyent.us postfix/smtpd[11790]: [ID 197553 mail.info] NOQUEUE: reject: RCPT from unknown[64.62.247.3]: 550 5.1.0 <apache@localhost.localdomain>: Sender address rejected: User unknown in local recipient table; from=<apache@localhost.localdomain> to=<mail+***************************@mailto.*******.com> proto=ESMTP helo=<smtprelay.livebooks.com>
I'm certainly no postfix aficionado, and am uncertain what steps to take here. Does something need to be further re/configured from our end? Is this an issue with the recipient's mail server that we should make them aware of? Any advice on first steps or a general explanation of what's going on here are much appreciated.