Greylisting is an anti-spam technique where servers temporarily reject mail from unknown senders. Learn how greylisting works and how it affects delivery timing.
Greylisting is an anti-spam method where a receiving server temporarily rejects an email from an unfamiliar sender. Legitimate mail servers usually retry delivery after a short delay, while many spam systems do not, which reduces spam volume.
When greylisting happens, the email may be delayed rather than permanently rejected. This can look like a soft bounce or a transient SMTP error, and the message may arrive later after retries.
If you see frequent greylisting, it can indicate a new or low-reputation sender identity. Improving authentication, warming up sending patterns, and maintaining clean lists can reduce the likelihood of repeated delays.