Red Hat Bugzilla – Bug 58201
Host name lookup failures in sendmail
Last modified: 2007-04-18 12:38:57 EDT
From Bugzilla Helper:
User-Agent: Mozilla/4.0 (compatible; MSIE 5.5; Windows NT 5.0)
Description of problem:
Host name lookup failures occur intermittently which causes some messages to
remain in queue. Some process through and some don't. Nslookups all work fine.
Name servers appear to have no problem.
Running sendmail RPM version 8.11.6-3
Version-Release number of selected component (if applicable):
Steps to Reproduce:
2.Intermittently some outgoing mail has host lookup failures.
Actual Results: Mail remains in queue and is not send. Bouncing sendmail
causes some messages to go through.
Expected Results: All messages get sent except when there really is a problem
Ok, problem's fixed. I think it was DNS. I tried all our DNS servers but all
had problems with getting nameserver lookup deferred with sendmail. So I just
installed a DNS cache server on the machine, and now it's all perfect.
Basically, it's a DNS server that runs on 127.0.0.1 and then I pointed
my /etc/resolv.conf to use that local server. The local server uses our office
DNS servers, but it's more robust and also caches the results. As soon a I put
this thing on, all the pending email whooshed right through. Could this still
be looked into with that in mind?
I have the exact same problem (host name lookup failures), but (so far) only
with mail going to hotmail.com. And, as far as I can tell, all mail going to
hotmail.com is affected:
[hotdog@mona ~]$ /usr/sbin/sendmail -bp
/var/spool/mqueue (11 requests)
----Q-ID---- --Size-- -----Q-Time-----
g272kX320367 2249 Thu Mar 7 03:54 MAILER-DAEMON
(Deferred: Name server: mx07.hotmail.com.: host name lookup
[...9 more emails going to various hotmail.com-addresses...]
g24FZu225755 191 Mon Mar 4 16:35 <firstname.lastname@example.org>
8BITMIME (Deferred: Name server: mx06.hotmail.com.: host name lookup
[Email-adresses have been obscured to protect the innocent]
However, I have no problem looking up hotmail.com, both the normal way and with
[hotdog@mona ~]$ nslookup
Default Server: dns1.cybercity.dk
Addresses: 184.108.40.206, 220.127.116.11, 18.104.22.168, 22.214.171.124
> set type=mx
hotmail.com preference = 5, mail exchanger = mx10.hotmail.com
hotmail.com preference = 5, mail exchanger = mx11.hotmail.com
hotmail.com preference = 5, mail exchanger = mx12.hotmail.com
hotmail.com preference = 5, mail exchanger = mx13.hotmail.com
hotmail.com preference = 5, mail exchanger = mx14.hotmail.com
hotmail.com preference = 5, mail exchanger = mx15.hotmail.com
hotmail.com preference = 5, mail exchanger = mx01.hotmail.com
hotmail.com preference = 5, mail exchanger = mx02.hotmail.com
hotmail.com preference = 5, mail exchanger = mx04.hotmail.com
hotmail.com preference = 5, mail exchanger = mx05.hotmail.com
hotmail.com preference = 5, mail exchanger = mx06.hotmail.com
hotmail.com preference = 5, mail exchanger = mx07.hotmail.com
hotmail.com preference = 5, mail exchanger = mx08.hotmail.com
hotmail.com preference = 5, mail exchanger = mx09.hotmail.com
Authoritative answers can be found from:
hotmail.com nameserver = ns1.hotmail.com
hotmail.com nameserver = ns2.hotmail.com
hotmail.com nameserver = ns3.hotmail.com
hotmail.com nameserver = ns4.hotmail.com
mx10.hotmail.com internet address = 126.96.36.199
mx11.hotmail.com internet address = 188.8.131.52
mx12.hotmail.com internet address = 184.108.40.206
mx13.hotmail.com internet address = 220.127.116.11
mx14.hotmail.com internet address = 18.104.22.168
mx15.hotmail.com internet address = 22.214.171.124
Also, I can telnet directly to mx02.hotmail.com:
[hotdog@mona ~]$ telnet mx02.hotmail.com 25
Connected to mx02.hotmail.com.
Escape character is '^]'.
220-HotMail (NO UCE) ESMTP server ready at Fri, 08 Mar 2002 01:26:57 -0800
220 ESMTP spoken here
221 Service closing transmission channel
Connection closed by foreign host.
Only sendmail can't seem to make the connection :-(.
For what it's worth, I'm using RedHat 7.0 (kernel 2.2.19-7.0.12 on an i486) with
Looks all more like Internet problems or DNS issues. Please reopen if you can
point at any wrong code within sendmail.
Florian La Roche
This happens on Redhat 7.2 AND on skipjack. DNS failures are occurring, but dig,
host, etc resolve the domains fine. There seems to be a problem in sendmail.
I too solved the problem by installing a DNS caching server on our system. The
problem appears not to be with sendmail as such, but with hotmail being
_really_ impatient at some times.
Try to telnet to one of the hotmail-mx-servers on port 25 and pretend to want
to send an email. Unless you cut'n'paste your commands, you'll get
disconnected - as far as I can tell only for being too slow.
Sendmail appears to be make some dns-lookup(s) after it connects to
mx__.hotmail.com (or any other server), and the dns-lookup)s= needs to happen
really fast or hotmail will disconnect the sendmail-process. Therefore, a local
DNS caching server will help. Well, at least from the second time, you try to
send an email to hotmail, since the caching server still needs to make a lookup
the first time :-).
I installed a DNS caching software to solve the problem. In this case, the
problem is related to sendmail on the Linix machine sending out. The example
given of Hotmail.com may be unrelated. By the time your Linux machine has been
able to connect to hotmail.com's MX servers on port 25, it's already completed
the DNS lookup. The problem is getting the DNS lookup to work succesfully. Once
you've made the port 25 connection, everything's fine.