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I am having trouble with a newly installed server that we have just migrated to. I am running sendmail and cannot send mail to a specific domain. Mail everywhere else appears to work. Logs say:

DSN: Service unavailable

Weirdly, I get a Message accepted for delivery and then a following entry to say DSN: Service Unavailable.

Why would this be? I do not have it relaying through a smart host. The server that I am sending from does not have a public IP and is purely for sending mail from a PHP application.

Any advice appreciated as Google hasn't been a big help.

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Do you have something else in your logs? – dave Aug 23 '12 at 12:33
I suspect you don't actually know what DSN means. Sendmail is telling you that it tried to send the message using the ESMTP extended syntax, but the remote server didn't like that. – adaptr Aug 23 '12 at 12:37
One possibility: the remote server thinks you're spamming, or is greylisting you. – cjc Aug 23 '12 at 13:24
Are you sure you don't mean DNS? A DSN is something used to connect to databases. It's not a service. – John Gardeniers Aug 23 '12 at 14:17
DSN can also stand for Delviery Status Notification (RFC 3461 - – dunxd Aug 23 '12 at 15:18

It might have mx record setup issue. Run the following command:

dig mx

where is your domain name.

In the output you will see Question section it is question to find the MX. In answer section you will find the mx entries configured for the domain. Check the mx records if they are correct.

Sample output is given below: where there 3 mx record entries like, etc


;; ANSWER SECTION: 3600 IN MX 10 3600 IN MX 20 3600 IN MX 30

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