sendmail: Host Unknown (host not found)

mfoley · 07-22-2017, 10:37 PM

I am sending a email from one Linux host to another on the same 192.168.0.0/14 LAN. On the source host, I have define(`SMART_HOST',`192.168.0.15')dnl, where 192.168.0.15 is the mail server for the LAN, also running sendmail. On the source host I get the maillog messages shown below. In particular is the message, "DSN: Host unknown (Name server: 192.168.0.15: host not found)." I don't understand why this host is not found, especially since I've specified the SMART_HOST by IP. I can ssh to this host by IP and hostname (server) and generally access it otherwise.

In the SMART_HOST /etc/mail/access I have "192.168.0 RELAY".

No messages whatsoever show up in the smart host's maillog, so it's not getting that far.

Why can't I send mail through it?

Code:

Jul 22 23:27:09 quadmon sendmail[2927]: v6N3R9c8002927: from=noreply@novatec-inc.com, size=317, class=0, nrcpts=1, msgid=<5974178d.vKxE2JDybzKGuOYE%noreply@novatec-inc.com>, relay=root@localhost
Jul 22 23:27:09 quadmon sm-mta[2928]: v6N3R9hg002928: from=<noreply@novatec-inc.com>, size=477, class=0, nrcpts=1, msgid=<5974178d.vKxE2JDybzKGuOYE%noreply@novatec-inc.com>, proto=ESMTP, daemon=MTA, relay=localhost [127.0.0.1]
Jul 22 23:27:09 quadmon sendmail[2927]: v6N3R9c8002927: to=mfoley@novatec-inc.com, ctladdr=noreply@novatec-inc.com (0/0), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30317, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (v6N3R9hg002928 Message accepted for delivery)
Jul 22 23:27:09 quadmon sm-mta[2930]: v6N3R9hg002928: to=<mfoley@novatec-inc.com>, delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=120477, relay=192.168.0.15, dsn=5.1.2, stat=Host unknown (Name server: 192.168.0.15: host not found)
Jul 22 23:27:09 quadmon sm-mta[2930]: v6N3R9hg002928: v6N3R9hg002930: DSN: Host unknown (Name server: 192.168.0.15: host not found)
Jul 22 23:27:09 quadmon sm-mta[2930]: v6N3R9hg002930: to=<noreply@novatec-inc.com>, delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=31702, relay=192.168.0.15, dsn=5.1.2, stat=Host unknown (Name server: 192.168.0.15: host not found)
Jul 22 23:27:10 quadmon sm-mta[2930]: v6N3R9hg002930: v6N3R9hh002930: return to sender: Host unknown (Name server: 192.168.0.15: host not found)

bathory · 07-23-2017, 08:26 AM

Quote:

I am sending a email from one Linux host to another on the same 192.168.0.0/14 LAN. On the source host, I have define(`SMART_HOST',`192.168.0.15')dnl, where 192.168.0.15 is the mail server for the LAN, also running sendmail.

Make sure that the nameserver defined in client's /etc/resolv.conf can resolve 192.168.0.15 to a valid hostname.
Or you can enclose the smarthost IP in square brackets, so sendmail doesn't do a dns lookup for it:

Code:

define(`SMART_HOST',`[192.168.0.15]')dnl

Don't forget to build sendmail.cf and restart the service.

Regards

RPN · 07-30-2017, 08:24 PM

I have a similar installation where users on one server needed mail forwarded to another server for either users on that mail server or to be sent off the LAN via the Internet.
One thing I had to do that you do not mention you have done is put an entry in the source server's /etc/hosts file pointing to the destination server which is also the main mail server for the domain. If you do not have an entry like the following in your /etc/hosts file you might give it a try.

Code:

192.168.0.15    novatec-inc.com  servername.novatec-inc.com