What is a retry policy?

A retry policy governs how your MTA handles messages that couldn't be delivered on the first attempt. It answers: how long do we keep trying, and how often?

Key components:

Queue lifetime: Maximum time a message stays in queue before being bounced as undeliverable. The standard is 5 days (RFC 5321 recommendation), though some systems use shorter periods for time-sensitive mail.

Retry intervals: How frequently to attempt redelivery. Typically starts frequent (every 5-15 minutes) and gradually extends (every 1-4 hours) using exponential backoff. This respects recipient servers while still attempting delivery.

Maximum attempts: Some policies limit total retry attempts regardless of time elapsed.

In Postfix, you configure this with:

maximal_queue_lifetime = 5d

minimal_backoff_time = 300s

maximal_backoff_time = 4000s

Aggressive retry policies (frequent attempts, long lifetimes) may annoy recipient servers. Conservative policies might give up too quickly on temporary issues. Balance persistence with courtesy.

The policy decides how long your ship waits at a closed port before sailing home.