Sending mail using Sendmail : DSesmtp setting

Question

Need some clarification on Mail Settings. We are managing around hundreds of applications. These applications runs on Linux based hosts and used to send mails to users based on user registration at site and other actions.

We have Sendmail configured on these Linux servers to relay mails to destination mailbox. The following setting is being used in sendmail.cf to forward mails to relay mail server.

        DSesmtp:xmail.example.com

This is fine for me. But on some servers , I can see only sendmail is running but the above settings is not enabled. But still mails are going through this server. I tried to send mails to Yahoo and GMAIL accounts and mails are successfully getting delivered.

   Aug 31 03:36:12 vmprod sendmail[23396]: u7V7aCMr023396: from=<admin@vmprod.wiley.com>, size=534, class=0, nrcpts=1, msgid=<201608310736.u7V7aCee023393@vmprod.wiley.com>, proto=ESMTP, daemon=MTA, *relay=localhost [127.0.0.1]*
   Aug 31 03:36:12 vmprod sendmail[23393]: u7V7aCee023393: to=queszama@yahoo.in, ctladdr=admin (35014/10), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30220, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (u7V7aCMr023396 Message accepted for delivery)
   Aug 31 03:36:13 vmprod sendmail[23398]: STARTTLS=client, relay=mx-apac.mail.gm0.yahoodns.net., version=TLSv1/SSLv3, verify=FAIL, cipher=RC4-SHA, bits=128/128
   Aug 31 03:36:16 vmprod sendmail[23398]: u7V7aCMr023396: to=<queszama@yahoo.in>, ctladdr=<admin@vmprod.wiley.com> (35014/10), delay=00:00:04, xdelay=00:00:04, mailer=esmtp, pri=120534, *relay=mx-apac.mail.gm0.yahoodns.net*. [106.10.166.52], dsn=2.0.0, stat=Sent (ok dirdel)

No Postfix,Exim running on this host

  -bash-4.1$ ps -ef | grep postifx
  essadmin  8974 20942  0 06:20 pts/4    00:00:00 grep postifx
  -bash-4.1$ ps -ef | grep exim
   essadmin  8982 20942  0 06:20 pts/4    00:00:00 grep exim

/etc/resolv.conf is pointing to a valid DNS server .

   $ cat /etc/redhat-release
   Red Hat Enterprise Linux Server release 6.3 (Santiago)

I am confused how mails are getting delivered since SMARTHOST is not configured . Any pointers ?

Answer 1

The system might be using an alternative to sendmail, like postfix or exim.

Check with the following command (as root):

netstat --tcp -lnp | grep :25

You will get something like:

tcp        0      0 127.0.0.1:25            0.0.0.0:*               LISTEN      1464/master
tcp        0      0 ::1:25                  :::*                    LISTEN      1464/master

Then check who this is with:

ps -aef | grep 1464 # replace 1464 with your pid

I get the following for instance:

root      1464     1  0  2015 ?        00:01:35 /usr/lib/postfix/master -w
postfix   1468  1464  0  2015 ?        00:00:25 qmgr -l -t fifo -u
postfix  25106  1464  0 09:13 ?        00:00:00 pickup -l -t fifo -u