Centos – How to configure sendmail to use a different SMTP server

centosexchangesendmail

I'm trying to configure sendmail on Centos 5 so that all mail goes through another SMTP server. In this case, it happens to be an Exchange Server. I've edited the sendmail.mc file with this line:

define(`SMART_HOST', `10.1.1.30')dnl

But when I try to send an e-mail, I get the following error:

Nov  2 14:02:00 COMPUTERNAME sendmail[1370]: oA2K1xht001368: to=<testemail@test.com>, ctladdr=<root@localhost.localdomain> (0/0), delay=00:00:01, xdelay=00:00:00, mailer=relay, pri=120355, relay=10.1.1.30, dsn=5.1.2, stat=Host unknown (Name server: 10.1.1.30: host not found)

The box 10.1.1.30 is accessible from the box I am sending mail from. Meaning, I can ping 10.1.1.30 and get good responses. So I don't understand why sendmail can't find the host. Any ideas? Thanks.

Best Answer

Sendmail appears to be doing a name lookup on '10.1.1.30'. Change the sendmail.mc to point to a hostname. If the hostname isn't in DNS you can put it into /etc/hosts.

Related Solutions

Sendmail: SMTP host name lookup failure

I'm going out on a bit of a limb here, but I think the problem is your remote host ...

getmxrr(smtp-server.nycap.rr.com, droplocalhost=1)
getmxrr: res_search(smtp-server.nycap.rr.com) failed (errno=110, h_errno=2)
<zeno@biyg.net>... Deferred: Name server: smtp-server.nycap.rr.com: host name lookup failure

It looks like res_search is the culprit here and what it's searching for (smtp-server.nycap.rr.com) is producing the error. According to netdb.h (I think) that error is either non-authoritative host or SRVFAIL.

Checking dns, it does look like something's wrong with that host (please forgive the use of nslookup) :

Non-authoritative answer:
Name:   smtp-server.nycap.rr.com
Address: 75.180.132.33

nslookup
> set q=ptr
> 75.180.132.33

Non-authoritative answer:
33.132.180.75.in-addr.arpa      name = cdptpa-omtalb.mail.rr.com.

I want to say it looks like a forward/reverse mismatch, but I could be wrong. It could just be one bad entry in their mailcluster. I'm thinking the reason that it works in the debug mode is that ruleset 3 is skipped and part of that ruleset is doing reverse lookups on the destination mailserver.

You might be able to solve this with a mailertable, that would go a ways towards fingering DNS info as the culprit. Take a look at this -- Solving hostname lookup failures in sendmail

Linux Sendmail – How to Configure a Real Domain Name for Sender Address

I think I have just solved it. I have the following in /etc/hosts:

127.0.0.1 www.mydomain.com test.mydomain.com
127.0.0.1 cdn.mycdn.com
127.0.0.1 localhost.localdomain localhost myserver.com

What I need is to place myserver.com in front of the line with localhost.localdomain so that sendmail will think that it is using a real domain to send out the email.

Best Answer

Related Solutions

Sendmail: SMTP host name lookup failure

Linux Sendmail – How to Configure a Real Domain Name for Sender Address

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