Quick answer: Look your server IP up in the major blacklist aggregators (MXToolbox blacklist check, Spamhaus IP lookup) and, if you send to Gmail, register in Google Postmaster Tools. A listing explains rejected mail; delisting is done at the specific blacklist operator, after fixing the cause.
Overview
Receiving servers consult DNS-based blacklists (DNSBLs) and their own internal reputation systems before accepting mail. Your sending IP's history — including what previous tenants did with it — directly affects delivery. Checking reputation is the first diagnostic step for any delivery problem and a monthly hygiene habit for any self-hosted mail server.
Before you start
- Your server's public IPv4 (shown on the Client Area service page).
- Your sending domain name — domain reputation is tracked separately from IP reputation.
Step-by-step guide
- Run an aggregate check: enter the IP at MXToolbox's blacklist tool — it queries dozens of DNSBLs at once.
- Check Spamhaus directly (the most influential lists: SBL, XBL, PBL) via their IP/domain checker.
- Query a DNSBL manually if you prefer the terminal:
(the IP is written in reverse order).# listed if the query returns 127.0.0.x dig +short 10.113.0.203.zen.spamhaus.org - For Gmail volume, add your domain to Google Postmaster Tools and watch the reputation graphs.
- If listed: identify the cause first (compromised script, open relay, purchased list), fix it, then follow that blacklist's delisting procedure. Delisting without fixing the cause leads to instant re-listing.
Common issues
- Listed on PBL: the Spamhaus Policy Block List is not an accusation — it marks ranges not expected to send mail directly; it matters only if you run your own MTA.
- Clean IP but poor Gmail delivery: domain reputation or engagement is the driver — see the deliverability checklist.
- Re-listed after delisting: the underlying spam source was not removed — audit the server for compromised sites and scripts.
When to contact support
If your IP was already listed when the service was delivered, or you have cleaned an incident and a listing will not clear, open a ticket with the blacklist name and lookup link — we will help on the network side.
Frequently asked questions
Which blacklists actually matter?
Spamhaus lists (SBL, XBL, PBL) carry the most weight with large providers; aggregate checkers like MXToolbox query dozens of lists at once and show everything relevant in one pass.
How do I get delisted from a blacklist?
Fix the root cause first — a compromised script, open relay or bad list — then follow the delisting procedure on that blacklist operator's site; unfixed causes lead to instant re-listing.
My IP is on the Spamhaus PBL — is that bad?
The PBL is a policy list marking ranges not expected to send mail directly; it only matters if you run your own mail server, and it is resolved through the Spamhaus self-service process.
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