Email error 451 4.7.1: Greylisted: try again later

What it means

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

1. Do nothing: a correct mail server retries and the message goes through.
2. Send from stable IPs so retries look like the same sender.
3. For urgent messages such as sign-in codes, use a provider with a stable sending identity.
4. Do not mark the address invalid because of this code.

How to prevent it

Most bounces come from addresses that were never checked. Verify each address before you send: syntax, domain, mailbox and risk are checked without sending a message. Test a single address with the free email checker or upload a whole list for bulk verification.

Verify an email address free · Clean a whole list · MX lookup · SPF, DKIM and DMARC checker

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

All email error codes