Permanent (5xx)
554 5.7.1
Message rejected due to policy
A hard policy rejection - often IP/domain blocklisting or an explicit sender block.
Common causes
- Sending IP is on a DNS blocklist.
- Receiving domain has explicitly blocked your sending domain.
What to do
- →Check your sending IP against major public blocklists (Spamhaus ZEN, Barracuda, SpamCop).
- →If newly delisted, warm the IP back up gradually rather than resuming full volume immediately.