Sending Infrastructure & Queues

Managing the "flow" of mail. You can't just send 1 million emails at once. This section explains queues (the holding area for mail) and throttling (pacing your sends) to avoid overwhelming mailbox providers, which looks like a spam attack.

13 questions in this topic

What are email queues? What causes emails to get stuck in queue? What is a retry policy? What is a deferred message (4xx error)? How does retry timing affect delivery? What are backoff algorithms in MTAs? How does load balancing work for large ESPs? What’s a rate limit and how do ESPs manage it? What’s the difference between 421 and 451 errors? How can ESPs detect and pause bad senders? What is greylisting and how does it affect queues? How do queues interact with reputation systems? How do “burst sends” differ from throttled batches?

Questions about Sending Infrastructure & Queues