Temporary failure (soft bounce)
Email error 451 4.7.1: Greylisted: try again later
The receiving server uses greylisting. It temporarily refuses mail from a sender it has not seen before and accepts it when the sender retries a few minutes later.
Common causes
- First contact between your server and the recipient server.
- The sending IP changes on every retry, so each attempt looks new.
- The recipient organisation has a strict anti-spam setup.
How to fix it
- Do nothing: a correct mail server retries and the message goes through.
- Send from stable IPs so retries look like the same sender.
- For urgent messages such as sign-in codes, use a provider with a stable sending identity.
- Do not mark the address invalid because of this code.
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Frequently asked questions
How long is the delay?
Often five to fifteen minutes, sometimes up to an hour.
Does it affect verification?
A verifier may see a temporary answer first. A good one retries and then reports the real result.
Other error codes
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