Queue retention and retry times
Email Security has a set of standard retry and retention times, which dictate how long an undelivered email will remain in the email queue.
If a connection results an error message in the 5xx range, the email will be deleted (as per the official RFC standards), and will not be retried. This is different for routes for which a connection cannot be made, or for error messages in the 4xx range: these will be retried until the email is greater than the retention policy.
Retention times
Retention time for inbound mail is set to 6 days. A NDR (Non-delivery Receipt) is not sent back to the remote sender on inbound emails.
Retention times for an outbound email is 4 hours. If the retention period does expire before successful delivery or the remote server replies with a 5xx error code a NDR is sent back to the sender.
Retry times
The retry times for both inbound and outbound emails is 30 minutes. If multiple routes exist for inbound emails each route is tried and if all fails the email is retried 30 minutes later.