Scenario:

What are the MX Outbound deferred mail settings?
What are the default SMTP queue deferred email settings?
What are the frequency of deferred mail delivery attempts?

Solution:

When an outgoing message is deferred on a MX outbound queue (SMTP Queue) the following intervals are practiced on delivery reties.

• 1st attempt is approx 5 min delay (from the timestamp of the original email when it arrived to us)
• 2nd attempt is approx 10 min
• 3rd attempt is approx 20 min
• 4th attempt is approx 40 min
• Any further attempts are approx 60 minutes until a max time on the queue of 5 days is reached and then the message is marked as failed.

For more information on deferred messages and retries please refer to SMTP RFC (RFC 2821), http://www.ietf.org/rfc/rfc2821.txt.

Note:

A message can be rejected/failed sooner depending on the SMTP error message from the down stream server.  Always best to check the log information for that message as it will give you an indication as to why it bounced.