How to setup and test SMTP AUTH within Sendmail

Solution Unverified - Updated -

Environment

  • Red Hat Enterprise Linux (RHEL)
  • Sendmail

Issue

  • How to setup and test SMTP AUTH within Sendmail

Resolution

1. Setting up SMTP AUTH:

  • Install following packages by using yum or update command. 
        cyrus-sasl-gssapi
        cyrus-sasl-md5
        cyrus-sasl
        cyrus-sasl-plain
        cyrus-sasl-devel
  • Start "saslauthd" service
        # service saslauthd start
        # chkconfig saslauthd on
  • Within the /etc/mail/sendmail.mc make sure following lines are uncommented 

        TRUST_AUTH_MECH(`EXTERNAL DIGEST-MD5 CRAM-MD5 LOGIN PLAIN'')dnl

        define(`confAUTH_MECHANISMS'', `EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN
        PLAIN'')dnl
  •   Run m4 command to rebuild the sendmail.cf file:
        # cp /etc/mail/sendmail.mc /etc/mail/sendmail.mc.orig
        # cp /etc/mail/sendmail.cf /etc/mail/sendmail.cf.orig
        # m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
  • Restart sendmail and saslauthd
        # service saslauthd restart
        Stopping saslauthd:                                        [  OK  ]
        Starting saslauthd:                                        [  OK  ]
        # service sendmail restart
        Shutting down sendmail:                                    [  OK  ]
        Shutting down sm-client:                                   [  OK  ]
        Starting sendmail:                                         [  OK  ]
        Starting sm-client:                                        [  OK  ]

2. Testing SMTP AUTH

  • To test SMTP AUTH from command line a valid username/password is required, following command uses username "test" and password "redhat" as example.

  • Generate base64 encoded string for username and password

       # echo -ne "\0test\0redhat" | base64
       AHRlc3QAcmVkaGF0
  • Telnet can be used to test SMTP AUTH by using above encoded string 

        # telnet 127.0.0.1 25
        Trying 127.0.0.1...
        Connected to localhost.localdomain (127.0.0.1).
        Escape character is ''^]''.
        220 dhcp.redhat.com ESMTP Sendmail 8.12.10/8.12.10; Wed, 24 Mar 2004
        13:03:57 -0500
        hello test
        250-dhcp.redhat.com Hello localhost.localdomain [127.0.0.1], pleased to
        meet you
        250-ENHANCEDSTATUSCODES
        250-PIPELINING
        250-8BITMIME
        250-SIZE
        250-DSN
        250-ETRN
        250-AUTH GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN
        250-DELIVERBY
        250 HELP
        auth plain AHRlc3QAcmVkaGF0
        235 2.0.0 OK Authenticated
        quit
        221 2.0.0 dhcp.redhat.com closing connection
        Connection closed by foreign host.
  • Note: Be sure to remove the pam_stack.so module if you are using RHEL 5 or newer.

For example /etc/pam.d/smtp:

#%PAM-1.0
auth       include      password-auth
account    include      password-auth

Diagnostic Steps

A possible issue is that if you have postfix also installed (a  known bug) - postfix will remove the needed pam smtp auth file, without  it SMTP-AUTH within sendmail will fail. Check to see if the following  file exists and has the following data within it (in fact my system had  postfix installed and so I needed to fix this during verification and  testing while witting this up) :

# cp /etc/pam.d/smtp.postfix /etc/pam.d/smtp
# cat /etc/pam.d/smtp
#%PAM-1.0
auth       required     pam_stack.so service=system-auth
account    required     pam_stack.so service=system-auth
#

The bugzilla on this issue can be found at:

https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=109313

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