How to Flush a Postfix Mail Queue

Many companies turn to Postfix as their mail transfer agent (MTA). As a free and open-source tool, Postfix is a reliable solution for routing and delivering electronic mail at scale. During routine administration, Postfix users may need to view, flush, and purge their mail queues. These actions are basic in concept but enable a user to manipulate the delivery, prioritization, and/or cancellation of an email.

Knowing how to manage a Postfix mail queue is very useful, especially if the recipient's email host defers or rejects messages. In this quick guide, you'll learn how to handle these administrative tasks and flush your mail queues with ease.

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View The Mail Queue

Before you can flush, purge, or otherwise manage your mail queue, you first need to look at which emails are currently sitting inside your mail queue. You can view your mail queue using the postqueue -p command.

mailhost01:~ user01$ postqueue -p

The results should resemble the following.

-Queue ID-  –Size– —-Arrival Time—- -Sender/Recipient——- 9DJF64JS935J*     319 Fri Dec 27 20:24:06  sender@test.com                                          recipient@test.com   78J3EIS0FH45*     319 Fri Dec 27 20:24:17  sender@test.com                                          recipient@test.com

The symbols at the end of the Queue ID provide information about the status of the email.

  • An exclamation mark ("!") notates that the queue status is on hold.
  • An asterisk (*) notates that the queue status is active.

Examine the queue and determine if you would like to flush or purge it.

Flush The Mail Queue

In order to flush your mail queue, you need to use the post queue -f command.

mailhost01:~ user01$ postqueue -f

When you use the flush command, the queue will attempt to redeliver all the emails remaining within it. Be wary of using the flush command too often, as multiple flushes can negatively affect your mail server's performance.

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Purge The Mail Queue

Purging allows you to remove an email from the queue. In order to purge your mail queue, you need to use the postsuper -d command, which can be executed in one of two ways.

  • Purge a single email using the postsuper -d [message id] command.
  • Purge all emails using the postsuper -ALL command.

Below is an example of using the first command to remove a single email from the queue.

mailhost01:~ user01$ postqueue -p -Queue ID-  –Size– —-Arrival Time—- -Sender/Recipient——- 9DJF64JS935J*     319 Fri Dec 27 20:24:06  sender@test.com                                          recipient@test.com   78J3EIS0FH45*     319 Fri Dec 27 20:24:17  sender@test.com                                          recipient@test.com   mailhost01:~ user01$ sudo postsuper -d 9DJF64JS935J postsuper: 9DJF64JS935J: removed postsuper: Deleted: 1 message

Below is an example of using the second command to remove all emails from the queue.

mailhost01:~ user01$ postqueue -p -Queue ID-  –Size– —-Arrival Time—- -Sender/Recipient——- 9DJF64JS935J*     319 Fri Dec 27 20:24:06  sender@test.com                                          recipient@test.com   78J3EIS0FH45*     319 Fri Dec 27 20:24:17  sender@test.com                                          recipient@test.com   mailhost01:~ user01$ sudo postsuper -d ALL postsuper: Deleted: 2 message

You can use the purge command as often as necessary without affecting the performance of your mail server.

Understanding Deliverability

The flush and purge commands come in handy when using Postfix as your MTA, but you must use them under the right circumstances. The need for these commands is often due to a recipient's host deferring or rejecting the emails you send out. When multiple emails are deferred or rejected, it will negatively impact your overall deliverability, harming your business' communications.

Sometimes, using a flush and attempting to redeliver the mail in the queue can increase overall deliverability for a given message. However, continuously trying to redeliver "undeliverable" mail can harm your mail server's reputation and its ability to deliver emails in the future.

If you're concerned about deliverability, there are other steps you can take as a company to improve the rate of delivery for your emails. Scheduling your emails at the right time, implementing a sender policy framework (SPF), sending emails consistently, and using double opt-in can all help improve deliverability.

Lastly, be certain that you are keeping your email lists purged of duplicate, inactive, and invalid recipients. The "cleaner" your email list, the less likely you are to find emails sitting in your mail queue waiting to be flushed or purged.

How to Flush a Postfix Mail Queue

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