What does it mean when an email is “deferred”?
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You send an email, check your logs a few hours later, and see it marked as "deferred." Not delivered. Not bounced. Just... sitting there. Should you panic?
Probably not. A deferred email is one your sending server tried to deliver, hit a temporary refusal from the receiving server, and placed back in the queue to try again later. The receiving server essentially said "not right now" instead of "never." That's the key word: temporary.
Under the hood, the receiving server returned a 4xx SMTP response code (the temporary error range, as opposed to 5xx which means permanent rejection). Your sending server sees that code, holds the message, and retries on a schedule.
Common reasons a message gets deferred:
- Rate limiting. The receiving server is throttling how many messages it accepts from your IP at once.
- Server busy. Temporary capacity issue on the receiving end.
- Greylisting. Some servers intentionally delay first-time senders, then accept on retry. It's an anti-spam technique.
- Reputation checks. The receiving server is being cautious about your domain or IP and asking your server to slow down.
- Temporary network problems. Connectivity hiccups between the two servers.
After a deferral, your sending server waits and tries again. Most ESPs use exponential backoff, meaning they wait longer between each retry attempt (5 minutes, then 30, then a few hours, and so on). This is normal behavior and it happens automatically. You don't need to manually resend anything.
If retries keep working, the message eventually delivers and you'd never know there was a hiccup. If the message can't be delivered after the maximum retry period (often 24 to 72 hours depending on your ESP), it gives up and generates a non-delivery report. At that point it becomes a bounce.
When should you worry? A handful of deferrals here and there is normal. If you're seeing a large percentage of your campaign deferred, especially after sending to a cold or old list, that's worth investigating. It can signal a reputation issue with your sending domain or IP. That's the moment to dig into your logs and look at the actual error messages attached to those deferrals.
Not sure whether what you're seeing is a normal blip or something bigger? Our SOS hotline is free and we're happy to take a look.
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