How to Enable Logging for Email Subject Fields in Postfix Maillog

Postfix MTA basically just capture ‘From’ and ‘To’ field while the subject is not logged to the maillog. There are simple steps to enable logging of the e – mail subject in postfix maillog. This will very useful for email administrators when performing troubleshooting of problems related with email.

1. Assume that postfix has been installed. Open the postfix main configuration file :
# vi /etc/postfix/
2. Uncomment the following :
header_checks = regexp:/etc/postfix/header_checks
3. Open /etc/postfix/header_checks file and add the following line at the bottom :
# vi /etc/postfix/header_checks
/^Subject:/     WARN
4. Run postmap to apply the new configuration in /etc/postfix/header_checks :
# postmap /etc/postfix/header_checks :
5. Restart or reload postfix configuration :
# service postfix restart


# postfix reload
6. Test send email with subject:test-ABC :
# telnet localhost 25
Trying ::1...
Connected to localhost.
Escape character is '^]'.
220 centos66.ehowstuff.local ESMTP Postfix
250-SIZE 10240000
250 DSN
250 2.1.0 Ok
250 2.1.5 Ok
354 End data with .
250 2.0.0 Ok: queued as 196AD1FDEA
221 2.0.0 Bye
Connection closed by foreign host.
7. Please confirm that the subject “test – ABC” is appearing in the log :
# tail -f /var/log/maillog
Apr  6 23:41:28 centos66 postfix/smtpd[4919]: connect from localhost[::1]
Apr  6 23:41:58 centos66 postfix/smtpd[4919]: 196AD1FDEA: client=localhost[::1]
Apr  6 23:42:07 centos66 postfix/cleanup[4924]: 196AD1FDEA: warning: header subject:test-ABC from localhost[::1]; from= to= proto=ESMTP helo=
Apr  6 23:42:07 centos66 postfix/cleanup[4924]: 196AD1FDEA: message-id=<20150406154158.196AD1FDEA@centos66.ehowstuff.local>
Apr  6 23:42:07 centos66 postfix/qmgr[4914]: 196AD1FDEA: from=, size=365, nrcpt=1 (queue active)
Apr  6 23:42:09 centos66 postfix/smtpd[4919]: disconnect from localhost[::1]


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