[SOLVED] sendmail ignoring MX records; only uses smart relay

lrtward · 03-03-2011, 09:56 AM

This is a new installation of CentOS 5.5
It is a web server that only needs to send out messages.
Some messages go to faculty and staff at domain.edu.
Other messages go to students at sub.domain.edu.

The mail server (Exchange) at domain.edu is my smart relay.
It rejects all mail not to user@domain.edu addresses.
Consequently, my web server cannot send messages to student@sub.domain.edu.

This problem also happens when sending to other domains such as gmail.com

/var/log/maillog:

Code:

Mar  3 10:42:30 webserver sendmail[17342]: p23FgUHB017342: from=<root@webserver.domain.edu>, size=320, class=0, nrcpts=1, msgid=<201103031542.p23FgSnA017341@webserver.domain.edu>, proto=ESMTP, daemon=MTA, relay=localhost.localdomain [127.0.0.1]
Mar  3 10:42:30 webserver sendmail[17341]: p23FgSnA017341: to=student@sub.domain.edu, ctladdr=root (0/0), delay=00:00:02, xdelay=00:00:00, mailer=relay, pri=30005, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (p23FgUHB017342 Message accepted for delivery)
Mar  3 10:42:30 webserver sendmail[17344]: STARTTLS=client, relay=smartrelay.domain.edu., version=TLSv1/SSLv3, verify=FAIL, cipher=AES128-SHA, bits=128/128
Mar  3 10:42:35 webserver sendmail[17344]: p23FgUHB017342: to=<student@sub.domain.edu>, ctladdr=<root@webserver.domain.edu> (0/0), delay=00:00:05, xdelay=00:00:05, mailer=relay, pri=120320, relay=smartrelay.domain.edu. [10.102.14.27], dsn=5.7.1, stat=User unknown

My web server can see the MX record for sub.domain.edu:

Code:

# dig -t mx sub.domain.edu

; <<>> DiG 9.3.6-P1-RedHat-9.3.6-4.P1.el5_5.3 <<>> -t mx sub.domain.edu
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 44489
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 2

;; QUESTION SECTION:
;sub.domain.edu.             IN      MX

;; ANSWER SECTION:
sub.domain.edu.      3600    IN      MX      0 1198448495.mail.outlook.com.

;; ADDITIONAL SECTION:
1198448495.mail.outlook.com. 300 IN     A       65.54.188.78
1198448495.mail.outlook.com. 300 IN     A       65.54.188.109

One last thing:

Code:

# echo '3,0 student@sub.domain.edu' | sendmail -bt
ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>
> canonify           input: student @ sub . domain . edu
Canonify2          input: student < @ sub . domain . edu >
Canonify2        returns: student < @ sub . domain . edu . >
canonify         returns: student < @ sub . domain . edu . >
parse              input: student < @ sub . domain . edu . >
Parse0             input: student < @ sub . domain . edu . >
Parse0           returns: student < @ sub . domain . edu . >
ParseLocal         input: student < @ sub . domain . edu . >
ParseLocal       returns: student < @ sub . domain . edu . >
Parse1             input: student < @ sub . domain . edu . >
Mailertable        input: < sub . domain . edu > student < @ sub . domain . edu . >
Mailertable        input: sub . < domain . edu > student < @ sub . domain . edu . >
Mailertable        input: sub . glenville . < edu > student < @ sub . domain . edu . >
Mailertable      returns: student < @ sub . domain . edu . >
Mailertable      returns: student < @ sub . domain . edu . >
Mailertable      returns: student < @ sub . domain . edu . >
MailerToTriple     input: < smartrelay . domain . edu > student < @ sub . domain . edu . >
MailerToTriple   returns: $# relay $@ smartrelay . domain . edu $: student < @ sub . glenville . edu . >
Parse1           returns: $# relay $@ smartrelay . domain . edu $: student < @ sub . glenville . edu . >
parse            returns: $# relay $@ smartrelay . domain . edu $: student < @ sub . glenville . edu . >

Why is sendmail ignoring MX records and sending all mail to the smart relay host? How can I troubleshoot this?

mesiol · 03-03-2011, 10:18 AM

Hi,

you should check the following:

Does a smart relay configuration allow relay to other domains/hosts without using smart relay? How should you sendmail know for which hosts to use smart relay and for which not?

lrtward · 03-03-2011, 10:24 AM

Hmm... maybe I have a huge misconception then. I thought that sendmail only used the smart relay IF it could not directly route the message itself.

I will test this out. Thanks for the idea.

lrtward · 03-03-2011, 10:28 AM

Boy, do I feel dumb! Yes that's what's happening.

I removed the smart relay entry and now my emails go directly to the destination host... where the connection is promptly refused

But I know why that is. This is a new test server, no external IP, no PTR records, not visible at all to the outside world. I'd refuse me, too, come to think of it. That I can work on.

Thanks for pointing out the embarrassingly obvious; much appreciated!