About exim tutorial

Exim is a mail transfer agent (MTA) used on Unix-like operating systems.

To print a list of the messages in the queue:
# exim -bp

To remove all messages from the queue:
# exim -bp | exiqgrep -i | xargs exim -Mrm

Testing email with exim
# exim -v 'user@domain'
# message here
# ^D ( control D )

This will use exim from the command line to create an email message To: user@domain. After typing the message, use Control+D to send the EOF (end of file) characters to exim. Exim will stop receiving input from the command line and send the message text to user@domain.

How to limit the number of emails sent by each user (prevent spammer) with DA.
http://help.directadmin.com/item.php?id=81