Postfix – subject, from and to log

This is a little trick for Postfix, it lets you log the subject, from and to of all the emails postfix sends (or which pass through it if you run it as a relay). It comes in handy when you need to debug an email issue and need to confirm your mailserver has sent the message.

First create the file /etc/postfix/header_checks and insert this into it:

/^subject:/      WARN
/^to:/           WARN
/^from:/         WARN
/^Subject:/      WARN
/^To:/           WARN
/^From:/         WARN

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Diplaying Logs with journalctl [CentOS7]

To simply view the logs on your system, you can execute the following command:


This will display the logs with the oldest entries first. Although this is simple, it is not very useful since we do not tend to read logs like a book.

By default journalctl displays the logs in a pager. It shows you one page of logs requiring you to hit the space bar to proceed.

Diplaying Logs by Date (more…)

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Iptables log connection

Here is an example to log new tcp connections (port 22):

-A INPUT -m state –state NEW -m tcp -p tcp –dport 22 -j LOG –log-prefix “New Connection: ” –log-level 4

Here is an example to log any tcp connections:

iptables -A INPUT -m state --state NEW -j LOG --log-prefix "New Connection: "
iptables -A OUTPUT -m state --state NEW -j LOG --log-prefix "New Connection: "


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