StatsDawg

This tracks the amount of mail in the 5 main Postfix mail queues:

• Mail Drop, which is mail collected from the sendmail utility (likely from a PHP script) but has not yet been processed by Postfix
• Hold, which is where e-mail fiting a definable criteria go, such as mail which fails an access policy or header/body check.
• Incoming, where messages first go to begin beign processed by the mail system.
• Active, which is mail that is basically queue for delivery. Unlike other queues, which are disk-based, the envolope information of the messages in this queue is resident in memory. This is also similar to the operating system process run-queue and can be thought of as such.
• Deferred, which contains e-mail that could not reach one or more recipients (such as due to SMTP delays, mail congestion, etc.)

More information about the different queues, and the utility that this information is collected from (qshape.pl) can be found at: http://www.postfix.org/QSHAPE_README.html

Most systems which process a small to moderate amount of e-mail may not see much use in this graph since Postfix is very efficient at dealing with large amounts of e-mail. For the larger and more complicated installations, however, this may help determine mail bottlenecks and give an overview of the performance of the mail system (or if someone is using the server as an open-relay, for instance).