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I have a CentOS server that runs postfix and whenever a null recipient is sent to it, the server freaks out. Instead of simply rejecting the mail, it doesn't know what to do with it and tries over and over again and if enough of these pile up, then it pegs the CPU.

The front end is from a vendor and apparently cannot be changed so I'm stuck with this crappy problem. The users don't enter an email address and it comes unglued.

What can I change in my postfix config that will automatically reject these null recipient addresses?

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Exactly what is Postfix doing? "Freaks out" is not a technical term... – Michael Hampton Sep 5 '13 at 21:16
It continually is attempting to figure out where to send the message, which cannot be sent. It's trying to find MX records for a null domain. – Brendan Sep 5 '13 at 21:25
Where are your log entries then? – Michael Hampton Sep 5 '13 at 21:26
This logs in maillog. What does that have to do with rejecting the null domain? – Brendan Sep 5 '13 at 21:31
This is not a forum and you should not treat it as such. You should provide at least as much information as necessary for us to figure out what your issue is, especially after being asked for it. Please see How can I ask better questions on Server Fault? for details on how to improve your question. – Michael Hampton Sep 5 '13 at 22:38

Postfix does know what to do with those messages: reject them, which is what it's doing. Your server may be under load, but it's trying to deliver a message for <> that it didn't accept in the first place.

You should really figure out why the client keeps trying to send messages to <> and have it stop doing that. It seems like the client is some sort of MUA. A proper MTA would have bounced the message back to sender after receiving a 5xx response.

client interaction

telnet 25
mail from: <>
250 2.1.0 Ok
rcpt to: <>
501 5.1.3 Bad recipient address syntax
221 2.0.0 Bye


Sep  5 15:00:43 server postfix/smtpd[22395]: connect from[]
Sep  5 15:01:09 server postfix/smtpd[22395]: warning: Illegal address syntax from[] in RCPT command: <>
Sep  5 15:01:21 server postfix/smtpd[22395]: disconnect from[]
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