550 5.7.1 Permanent Failure Message rejected due to policy (spam/content)
The message was rejected not because the mailbox doesn't exist, but because the receiving server's policy engine blocked it — commonly a spam-filtering or sender-reputation decision.
Common causes
- Sending IP or domain has poor reputation or is blocklisted.
- Message content triggered spam filtering.
- Missing or failing SPF/DKIM/DMARC authentication.
What to do
This is not a list-hygiene problem — investigate sender reputation and authentication (SPF/DKIM/DMARC) rather than removing the address, since the mailbox itself may be perfectly valid.
Provider note: Some providers (notably Gmail and Microsoft) use 5.7.1 broadly for a range of policy rejections, so the exact cause often requires reading any additional free-text detail included in the bounce message.
FAQ
Does this mean the email address is invalid?
No — this is a sender-side reputation/authentication/content issue, not confirmation the recipient address is bad. Treating 5.7.1 bounces the same as 5.1.1 (user unknown) is a common and costly misclassification.
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