"550 5.7.1 rejected — listed at Spamhaus": getting delisted

Receivers using Spamhaus reject at SMTP time with bounces like:

550 5.7.1 Service unavailable; client [203.0.113.25]
blocked using zen.spamhaus.org

zen.spamhaus.org is a combined list — the fix depends on which component actually lists you. SBL is human-curated spam sources, XBL is compromised machines and botnet traffic, and PBL is address space that simply should not send direct mail (residential/dynamic ranges) — a policy statement, not an accusation.

Diagnose it

Run the blocklist check below on your sending IP. ProbeKit queries each Spamhaus zone (and ~35 others) separately and shows the return code plus the listing reason, so you know whether you are dealing with SBL, XBL or PBL before visiting the delisting form. Note: these lookups must come from a non-public resolver — ProbeKit's hosted checker does this correctly.

Fix it

PBL: you are sending direct from an IP that is not supposed to send. Either relay through your provider's smarthost, or — if you legitimately run a mail server on this IP — use the PBL removal form; static business IPs are removed quickly.

XBL: something on your network is infected or proxying spam. Find and clean it first (check NAT logs for port-25 bursts) — delisting without fixing it just relists you within hours.

SBL: actual spam was observed. Stop the source (compromised account, purchased list, open relay), then answer the SBL ticket honestly — Spamhaus responds well to concrete remediation.

After delisting, add a blacklist monitor so a relisting alerts you before your users notice bounces.