The email message queue in Spam Control temporarily stores incoming emails when the destination mail server is not reachable. Emails are usually delivered directly to the destination server and are only queued in case of temporary delivery issues.
Table of Contents
- When are emails queued?
- When are emails not queued?
- What applies to catch-all configurations?
- How do I open the queue?
- When is delivery retried?
- What happens after 4 days?
- What does a frozen message mean?
- How long are valid recipients stored?
When are emails queued?
Emails are queued in Spam Control when the destination mail server is temporarily unreachable and the recipient is known as a valid recipient.
This can happen, for example, if the destination mail server is temporarily offline, there are network problems, or the destination route is temporarily unavailable.
In this case, Spam Control accepts the message and automatically attempts to deliver the email to the destination mail server again later.
When are emails not queued?
Emails are not queued if the destination mail server permanently rejects the message. This is typically the case with a 5xx error code.
In the case of a temporary error, the sending mail server usually receives a 4xx error code. In this case, the sending mail server should queue the message itself and retry delivery later.
What applies to catch-all configurations?
If the destination mail server operates as a catch-all for the domain, recipients are not automatically cached.
In this case, emails are only queued if the valid recipients have been explicitly stored in Spam Control.
How do I open the queue?
The queue can be opened via the Spam Control web interface. There you can see emails that are currently waiting for redelivery.
- Log in to Spam Control.
- Open the Incoming section.
- Open Queue for incoming mails.
- Check the messages waiting for redelivery.
In the web interface, you can also manually trigger redelivery of a message from the queue if needed.
When is delivery retried?
Messages in the queue are automatically redelivered if delivery failed due to a temporary problem with the destination mail server.
Spam Control uses approximately the following retry schedule:
- In the first 2 hours: Delivery is retried every 15 minutes.
- In the next 14 hours: Delivery is retried at a variable interval. The interval starts at 15 minutes and is multiplied by about 1.5 with each attempt.
- From 16 hours after the first failure up to a maximum of 4 days: Delivery is retried approximately every 6 hours.
What happens after 4 days?
If a message cannot be delivered after 4 days, delivery is considered permanently failed. Afterwards, a non-delivery report is generated for the sender.
If this non-delivery report cannot be delivered immediately, it is frozen. The original message will no longer be automatically delivered after the 4-day period.
The 4-day period corresponds to the usual behavior according to the SMTP standard. This allows the sender to learn that their message could not be delivered over an extended period.
What does a frozen message mean?
A message is considered frozen if it can neither be delivered to the recipient nor returned to the sender.
No automatic delivery attempts are made for frozen messages.
A super administrator can release frozen messages again and force new delivery attempts if the original problem has been resolved.
How long are valid recipients stored?
Spam Control caches known valid recipients for up to 4 days. This allows emails for these recipients to be accepted and queued in case of temporary problems with the destination mail server.
When this entry expires, new emails for these recipients are no longer cached by Spam Control. Instead, the message is temporarily rejected so that the sending mail server retries delivery later.
If you use the Local Recipients feature, no caching via the recipient cache takes place. Spam Control then continues to accept emails for the specified recipients and queues them in case of temporary delivery problems.
If the destination mail server becomes reachable again and the recipients are correctly configured, queued messages are automatically redelivered.