What is a block bounce?

A block bounce is rejection based on sender reputation or policy:

What it means:

The address exists and is valid. The receiving server is operational. Your message is specifically being refused. The problem is with you, not the recipient.

Common causes:

IP blocklisting: Your sending IP is on a blocklist. Domain reputation: Your domain has poor reputation. Content filtering: Message content triggered filters. Policy violation: Authentication or compliance failure.

Typical codes:

550 or 554 with policy or spam references. 5.7.1 (not authorized). Provider-specific block messages.

Key distinction:

Block bounces may be temporary (reputation can improve). Different from hard bounces where address is invalid. Requires investigation, not just suppression.

Block bounces say "we don't want mail from you." The destination exists; they just refuse your cargo.