Block bounce
A rejection caused by the sender rather than the address: the receiver refused the message because of IP or domain reputation, a blocklist listing, authentication or content.
What it means
Block bounces usually carry a 5.7.x enhanced status code (security or policy) or a provider's own policy code, often with a link explaining the block: 550 5.7.1 for a policy refusal, 5.7.26 for failed authentication checks, Microsoft's 5.7.708 for traffic not accepted from an IP. SendGrid calls these blocks and gives a deny list, an ISP blocking the IP, or a filter flagging the content as typical reasons; Postmark classifies them as a separate ISP block type.
The recipient's address is normally fine, so suppressing it fixes nothing, and SendGrid does not add blocked addresses to its suppression list. The fix is on the sending side: get delisted, correct SPF, DKIM or DMARC, slow down, or change the content.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- Twilio SendGrid Docs: Manage blocked messagestwilio.com
- Postmark API: Bounce typespostmarkapp.com
- IANA, SMTP Enhanced Status Codes registryiana.org
- Microsoft Learn: Email non-delivery reports and SMTP errors in Exchange Onlinelearn.microsoft.com
All 432 terms in the glossaryThe wiki: blocklists and bounce codes