Distribute triplets to other MX

[kmkaplan]

When a mail domain has multiple MX, when a sender tries to deliver to different ones the timer is set independantly in each MX. This can result in excessively long delay in delivery.

When an MX creates a new triplet it should also distribute it to other MX. The protocol for distribution could be based on UDP: this would be easy to implement. But this would cause difficulties regarding firewalls. An alternative would be to send them via SMTP (email). This is much more heavyweight but should work everywhere.