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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 postfix/smtpd[11790]: [ID 197553] NOQUEUE: reject: RCPT from unknown[]: 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=<>

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.

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up vote 3 down vote accepted

Your machine is referring to itself as localhost.localdomain. They're rejecting you based on that.

In your postfix, you should have "myhostname" and "mydomain" set correctly. You also might want to look at whatever is generating that email and making sure it's not putting the @localhost.localdomain in there.

For more help, please update with the output of "postconf -n" so that we can see your config.

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Well, to be more clear, we are simply the recipient of this email, not the sender. Another provider is sending this email to us, and we're rejecting it. So I take it the misconfiguration is on their side of things? – user28508 Dec 9 '09 at 15:04
Oh. Sorry, I didn't see that from your question. Specifically, the "Is this an issue with the recipient's mail server that we should make them aware of?" sounded like the recipient isn't you. Yes, tell the other side that their mail config is fatally damaged. Your site isn't the only one they can't get to. – Bill Weiss Dec 9 '09 at 16:14

This could be a problem with your configuration. Your postfix thinks 'localhost.localdomain' is local and checks if user 'apache' exists locally.

Since it does not exist, it rejects the email.

Check your smtpd_sender_restrictions to fix it.

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