SMTP/Postfix

Postfix

What is Postfix? An easy, fast, and secure SMTP server. Did I mention it was easy to configure?

Major Postfix specific configurations

• main.cf    => Specifies a very small subset of all the parameters that control the operation of Postfix. Parameters not explicitly specified are left at their default values. 
• master.cf => Defines how a client program connects to a service, and what daemon program runs when a service is requested.

To setup postfix need below rpm:

yum install postfix 
yum remove sendmail

The server acting as a mail transfer agent uses TCP port 123

Common Commands 

service postfix reload    => reload postfix configuration and hash tables

service postfix [restart, stop, start]    => stop/starts/restarts Postfix

mailq    => view the active mail queue (you can alternative run postqueue -p)

postcat -q <QID>    => View email that's in queue 

postqueue -f    => Reprocess messages in Queue and immediately retry delivery

postmap /etc/postfix/access    => Reload sender access list

postmap /etc/postfix/transport    => Reload Transport table

To kill one email

postsuper -d 56F7F20515

Save and close the file. Restart / reload postfix MTA:

# /etc/init.d/postfix restart

To concurrently watch emails:

watch -n1 mailq

To delete all email in the queue from a domain run this command as root:

postqueue -p | tail -n +2 | awk 'BEGIN { RS = "" } /@example\.com/ { print $1 }' | tr -d '*!' | postsuper -d -

To delete all email in the queue From: a specific email address run this command as root:

postqueue -p | tail -n +2 | awk 'BEGIN { RS = "" } /username@example\.com/ { print $1 }' | tr -d '*!' | postsuper -d -

TLS issue:

Add below to /etc/postfix/main.cf :
CASE 1 (Send TLS encrypted emails if supported else send without TLS):

smtp_tls_security_level=may

smtp_tls_loglevel=1

Comment below line:

smtp_tls_policy_maps = hash:/etc/postfix/tls_policy

Restart postfix: /etc/init.d/postfix reload

-----------------------------------------------------------------------------------
CASE 2 (Send encrypted emails only to google):
Update: /etc/postfix/tls_policy to contain below line:

gmail.com secure

Restart postfix: /etc/init.d/postfix reload