How long are emails kept in the Delivery Queue

In most cases, emails are delivered straight to the destination server. However, if the delivery attempt to the destination server returns a temporary failure, all email messages sent to known, valid recipients are queued locally on the filtering servers for delivery retry.

Emails which have been permanently rejected by the destination server with a 5xx error code, will NOT be queued and are rejected by the system.

Automatic Retry Schedule

If messages encounter temporary obstacles in their route to known valid recipients, such as network problems, they will be automatically retried for delivery at the following approximate intervals:

• During the first 2 hours, delivery is retried at an approximate interval of 15 minutes.
• During the next 14 hours, delivery is retried incrementally, starting at 1 hour and multiplying by 1.5 with each attempt.
• From 16 hours, until 60 days have passed since the initial failure, delivery is retried at an approximate interval of every 6 hours.
• After 60 days we generate a bounce to the sender. If the bounce cannot be delivered immediately (i.e. if the ‘message could not be delivered’ message (Non-Delivery Report) fails to send), it will be frozen automatically. After this time, delivery of the message will have permanently failed.

When a message is frozen (it cannot be delivered to the recipient or returned to the sender), no more automatic delivery attempts are made. An Admin user can force retry such messages when the problem has been corrected.

SpamBull stores valid recipients in its cache. Once the cache expires, it stops queuing emails for those recipients. The messages will be temporarily rejected, leading the sending server to retry delivery automatically.