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We have ubuntu 12.04 server and installed sendmail to send mails from this server.


There is some strange issue on mail server. Somehow, server not able to send email to

but server sends email successfully to other email ids like, or

Success Case: when send email to

Dec 28 11:40:49 ip-10-99-66-252 sm-mta[16954]: qBSBemdx016952: to=, ctladdr= (33/33), delay=00:00:01, xdelay=00:00:01, mailer=esmtp, pri=120352, [], dsn=2.0.0, stat=Sent (OK 1356694874 d3si34930711vdv.119) Dec 28 11:51:43 ip-10-99-66-252 sendmail[16960]: qBSBphki016960: from=www-data, size=89, class=0, nrcpts=1, msgid=<>, relay=www-data@localhost

Fail Case: when send email to

Dec 28 11:51:43 ip-10-99-66-252 sm-mta[16962]: qBSBphSo016962: ... User unknown Dec 28 11:51:43 ip-10-99-66-252 sendmail[16960]: qBSBphki016960:, ctladdr=www-data (33/33), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30089, relay=[] [], dsn=5.1.1, stat=User unknown

Can someone please help to sort out this issue ?

Note: I don't want to expose our emails that's why i replaced xxx with original email address into this question.

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The user unknown message means info is not a valid user at the domain

This is a permanent error and not something you can fix, as the email address (recipient) is rejected by this mail server.

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