Postfix Mail Queue Management

Like any other MTA , one of the important activity of Postfix is to handle Mail Queue. In Postfix architecture there are many processes involved to handle mail delivery task . Cleanup is one of the postfix processes and it performs task of putting mail into Incoming Queue.

Once the message enters into Incoming Queue , Queue Manager process become active and handle it . Queue manager process called as heart of Postfix mail system and it handle task of mail delivery . Queue manager process contact delivery agent . Delivery agents such as smtp,lmtp,local etc are those process who deliver mail to right address .

Postfix manages following types of Mail Queue

Incoming Queue

Once the message enters the system , no matter whether it entered via smtpd or qmqpd or any other means the message will placed in the Incoming Queue. The Cleanup process is the Postfix process which put s missing headers before placing the message in the queue .

Active Queue

Once the message placed into Incoming Queue , the queue manager process picks the message from Incoming Queue and place that message into Active Queue .This movement depend upon the resource limit of the Active Queue.

The concept of active queue has been taken to keep queue light for MTA processes. The Active Queue holds only those messages which are ready to be delivered . The most important point from performance point of view is that the Active Queue is kept in memory not on disk.

Postdrop

This mail queue holds the message which are sent via the local sendmail program . The mail recieved via smtpd or any other network interface never stored inside this queue.

Deferred

From my personal experiences of Sendmail MTA which doesn’t manage any separate queque for deferred mail , I can say keeping a separate queue for rejected mail is really a very good approach adopted by Postfix . The messages which are failed in delivery by Postfix are stored inside this Queue .

Hold

We can set a policy to keep the mail on hold for time being and then releases it . Any message that enters into this queue , remains here unless released by Administrator. This queue is helpful in the content inspection and header checking .

Corrupt Damaged queue files kept inside this queue .

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