How does retry timing affect delivery?

Retry timing directly affects both delivery success and your relationship with recipient servers.

Too aggressive: Hammering a server with constant retry attempts can trigger blocks or rate limiting escalation. Recipient servers may interpret rapid retries as abuse. You also waste resources on problems that need time to resolve (like a full mailbox needing user action).

Too conservative: Long gaps between retries mean messages take forever to deliver when the issue was brief. Time-sensitive emails may become irrelevant by the time they arrive. Users expect faster delivery.

Exponential backoff is the standard approach: start with short intervals (5 minutes), extend progressively (15, 30, 60, 120 minutes...). This balances quick recovery from brief outages against patience for longer issues.

Smart timing also varies by error type. Rate limiting (421, 450) might warrant faster retries as slots open. Server errors (451) might need longer waits for repairs.

Recipient servers notice retry patterns. Well-behaved senders using standard backoff earn goodwill; aggressive retry loops earn suspicion.

A polite knock becomes annoying when repeated every ten seconds. Space your attempts respectfully.