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This is a continuation of a previous question here: Sendmail won't send email to same domain

Initially I was having trouble getting a webserver (say domain.com) running Sendmail 8.14.4 on Ubuntu 13.10 to deliver a message to an address at the same domain name (say someone@domain.com). The mailserver is actually managed elsewhere - mail.domain.com points to a separate IP in the DNS. I have now changed the hostname of this webserver to www.domain.com and it appears to be reading the correct IP address of the mail server to send the message to, but I'm getting an User unknown error. The mail server has a forwarding address set up rather than an actual mailbox.

When logged into the webserver via SSH an nslookup of mail.domain.com returns the correct IP of the mail server. Although it returns Non-authoritative answer? Then when connecting to this IP via telnet the user email address is accepted so it appears the mailbox is setup correctly on the mailserver and there is something not working with sendmail?

The log is below:

Jan 27 12:13:31 www sendmail[1839]: s0RCDV3n001839: from=www-data, size=129, class=0, nrcpts=2, msgid=<201401271213.s0RCDV3n001839@www.domain.com>, relay=www-data@localhost
Jan 27 12:13:32 www sm-mta[1841]: s0RCDVtW001841: from=<www-data@www.domain.com>, size=401, class=0, nrcpts=2, msgid=<201401271213.s0RCDV3n001839@www.domain.com>, proto=ESMTP, daemon=MTA-v4, relay=localhost []
Jan 27 12:13:32 www sendmail[1839]: s0RCDV3n001839: to=someone@domain.com,someone@anotherdomain.com, ctladdr=www-data (33/33), delay=00:00:01, xdelay=00:00:01, mailer=relay, pri=60129, relay=[] [], dsn=2.0.0, stat=Sent (s0RCDVtW001841 Message accepted for delivery)
Jan 27 12:13:32 www sm-mta[1843]: STARTTLS=client, relay=spool.mail.gandi.net., version=TLSv1/SSLv3, verify=FAIL, cipher=DHE-RSA-AES256-SHA, bits=256/256
Jan 27 12:13:36 www sm-mta[1843]: s0RCDVtW001841: to=<someone@anotherdomain.com>, ctladdr=<www-data@www.domain.com> (33/33), delay=00:00:05, xdelay=00:00:04, mailer=esmtp, pri=150401, relay=spool.mail.gandi.net. [], dsn=2.0.0, stat=Sent (Ok: queued as 378B22A89BC)
Jan 27 12:13:36 www sm-mta[1843]: STARTTLS=client, relay=mail.domain.com., version=TLSv1/SSLv3, verify=FAIL, cipher=DHE-RSA-AES256-SHA, bits=256/256
Jan 27 12:13:36 www sm-mta[1843]: s0RCDVtW001841: to=<someone@domain.com>, ctladdr=<www-data@www.domain.com> (33/33), delay=00:00:05, xdelay=00:00:00, mailer=esmtp, pri=150401, relay=mail.domain.com. [], dsn=5.1.1, stat=User unknown
Jan 27 12:13:36 www sm-mta[1843]: s0RCDVtW001841: s0RCDatW001843: DSN: User unknown
Jan 27 12:13:37 www sm-mta[1843]: s0RCDatW001843: to=<www-data@www.domain.com>, delay=00:00:01, xdelay=00:00:01, mailer=local, pri=30000, dsn=2.0.0, stat=Sent
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