MTA queue

Manage MTA queue

The gateway uses Postfix for sending and receiving of email (MTA). The MTA queue can be viewed and managed from the “Mail transfer agent Queue” page.

The MTA queue contains emails which cannot be immediately delivered.

Delete selected

Delete the selected emails from the queue.

Hold selected

Put selected emails on hold, i.e., tells the MTA to no send those emails.

Release selected

Release selected emails which were previously put on hold.

Requeue selected

If an email is requeued, the email will be handled by the gateway as if it was a new email.


Flush the queue, i.e., attempt to deliver all queued mail.


By using a filter, emails which match the filter will be shown. This can be helpful if there are a large number of items in the queue.

Regular expression

If enabled, the filter is treated as a regular expression.

Email content

The content of a queued email can be viewed by clicking the Queue ID field of the email. The “raw” mail queue item will be viewed including Postfix meta information (for example the mail envelope details, client IP address etc).

MPA queue

The Mail Processing Agent (MPA) is the internal mail handler which is responsible for encryption, decryption, DLP etc.

The MPA contains four queues: “MPA outgoing”, “MPA error”, “MPA spool” and “MPA respool”.

MPA outgoing

The MPA outgoing queue contains the emails which have been handled by the MPA and are now waiting to be accepted by Postfix. MPA outgoing queue should normally be empty unless Postfix is too busy.

MPA error

The MPA error queue contains emails which could not be handled. This can happen for example if an email template is modified by the admin but the mail template is invalid. Under normal circumstances the error queue should be empty.

MPA spool

The MPA spool contains the emails which are being handled by the MPA. If the MTA accepts emails faster then the MPA can handle them, the MPA spool might grow.


If the MPA spool or error queue grows over certain limits, the MPA starts throttling email from the MTA. If the MPA spool directory exceeds 2000 emails, the MPA no longer accepts emails from the MTA. The mails will then queue up in the MTA.

MTA respool

The MTA respool contains items to be respooled. If an email is put into the MTA queue, the email can be moved to the MTA respool queue. If the issue, which resulted in the error, is resolved, for example the template is fixed, the email can be respooled.