SMTP 451 4.7.1: greylisting and temporary rejection

What the message looks like

451 4.7.1 <info@beispiel.de>: Recipient address rejected: Greylisted for 300 seconds

Common causes

• First contact with a new sender: Postgrey or Rspamd greylisting works as designed.
• Applications or devices (scanners, ticket systems) send directly without a queue and never retry.
• Large senders use IP pools, so each retry comes from a different IP and counts as new again.
• Other 4.7.1 policies, e.g. rate limits or temporary policy server errors.

Check

1. Find greylisting entries in the log
   journalctl -u postfix --since today | grep -i greylistCopy
2. Check whether greylisting is in the restrictions
   postconf smtpd_recipient_restrictionsCopy
3. Check Postgrey status
   systemctl status postgreyCopy
4. On the sending side: is the message still queued?
   postqueue -p | grep -B2 'Greylisted'Copy

Fix

• Wait: normally the message arrives after 5–15 minutes, no action needed.
• Whitelist important partners, for Postgrey in /etc/postgrey/whitelist_clients.local, then systemctl reload postgrey.
• Make applications send through a local MTA with a queue (Postfix as relay) instead of direct SMTP.
• Lower the greylisting delay (Postgrey --delay=60) or enable it in Rspamd only for poorly scored mail.

FAQ

Is 451 4.7.1 a problem on my side?

Usually not. Greylisting is the receiver's choice. It only becomes a problem if your system does not retry.

Does greylisting still make sense today?

It slows down simple spam bots but also delays legitimate mail like login codes. Many admins now use it only for mail with a medium spam score.