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Greylisting Temporary spam prevention

temporary Concept

Meaning

Greylisting is an anti-spam technique where a receiving server temporarily rejects an email from an unknown sender, expecting a legitimate mail server to retry delivery.

Common causes

  • You are sending an email to a specific recipient from a specific IP address for the first time.
  • The receiving server uses greylisting to block poorly written spam bots that do not implement retry logic.

How to fix

  1. Do nothing. Your Mail Transfer Agent (MTA) will automatically queue the email and retry sending it after a short delay (usually 5-15 minutes).
  2. Upon the second attempt, the receiving server will accept the email and 'whitelist' your IP for future sends.

Example bounce

451 4.7.1 Greylisted, please try again in 300 seconds.

FAQ

Does greylisting cause emails to be lost?
No, legitimate mail servers will always retry. The email will just be delayed by a few minutes.
How do I bypass greylisting?
You cannot bypass it on the first send. However, once you successfully deliver an email, the receiving server usually remembers your IP and won't greylist you again for that recipient.

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