TL;DR: Greylisting is an anti-spam trick where a receiving server temporarily rejects email from a sender it doesn't recognise, asking it to "try again later". Real mail servers retry and get through; many spam bots don't bother. The visible effect is that a first email can arrive a few minutes late — then everything is normal. Scan your domain free to make sure good authentication isn't the thing slowing you down.
How greylisting works
When a new sender (a unique combination of IP, sender and recipient) shows up, the receiving server replies with a temporary "try again" error instead of accepting the message. A legitimate mail server treats that as a normal soft deferral and retries minutes later — and this time it's accepted and remembered. Spam scripts that fire once and move on never come back.
Why providers use it
It's cheap and effective: it filters out a chunk of low-effort spam without any content analysis, just by exploiting the fact that bots usually don't retry. The cost is a small one-time delay on the very first message from a new sender.
Is greylisting a problem?
Usually not. It's normal behaviour and resolves itself. It only becomes annoying when you're waiting on a time-sensitive first email (a login code, a password reset) — which is why some providers skip greylisting for those.
What to do about it
- As a sender: make sure your mail system retries (all proper ones do) and sends from a consistent IP — switching IPs makes you "new" each time and re-triggers the delay.
- Authenticate well. Solid SPF/DKIM/DMARC and reputation help receivers trust you sooner.
- As a receiver: if first-message delays hurt you, ask your provider about tuning or disabling greylisting.
FAQ
How long is the greylisting delay?
Usually a few minutes to up to an hour, depending on the receiver's settings and your server's retry schedule.
Does greylisting cause bounces?
No — it's a temporary deferral, not a rejection. The mail is delivered on retry, not bounced.
Can I avoid it as a sender?
Not entirely, but a consistent sending IP and good reputation mean you're "known" quickly and rarely delayed again.
First emails arriving late and not sure why? Scan your domain, then reply to your report — we're developers and we'll check your sending setup and authentication.