Look up two things, not one: the IP your mail leaves from, and the domain in your From address. For the IP, check Spamhaus SBL and XBL, SpamCop and Barracuda. For the domain, check Spamhaus DBL and SURBL. If all of those are clean and your mail is still filtered, you do not have a blocklist problem, and the rest of this page explains what you do have.
Published by emailcampaign.ai, which runs sending infrastructure for cold outbound. We see far more placement problems caused by authentication and volume than by blocklists, and the ordering below reflects that.
Check the IP and the domain separately
These are two different reputations and they fail for different reasons. Mail sent from a listed IP is refused at connection time, usually with a bounce that names the list. A listed domain is filtered no matter which server sends it, which is why moving providers does not fix a domain listing.
To find the IP your mail actually leaves from, open a message you sent to yourself and read the last Received header, or check the SPF record if you send from your own server. People frequently look up their website host by mistake, which is a different machine entirely.
The lists worth reading
| List | What it lists | Who consults it | Weight |
|---|---|---|---|
| Spamhaus SBL / XBL / DBL | IPs and domains | Most major providers and many corporate filters | High |
| SURBL | Domains appearing in message bodies | Filtering appliances and some providers | Medium |
| SpamCop | IPs, from complaint feedback | A narrower set of receivers | Medium |
| Barracuda | IPs | Barracuda appliances, common in mid-market corporates | Medium |
| The long tail | IPs, often automatically | Very few, sometimes nobody | Low to none |
Multi-lookup tools query eighty or more lists and present every hit with equal weight. That is how a single listing on a list nobody queries turns into an afternoon of panic. Read the first two rows of the table above, then stop.
Blocklists explain fewer problems than people expect
Gmail and Outlook do not primarily filter by public blocklist. They use their own reputation data: whether recipients open, reply, delete without reading or mark as spam, whether your authentication aligns, and how your volume pattern compares to your history. A domain can be clean everywhere public and still land in spam at Gmail, and that is the ordinary case.
Run these four checks before you go looking for a listing:
- Does authentication resolve? Not "do the records exist" but do they evaluate. Two SPF records on one host is a permanent error. So is an include chain past ten DNS lookups. This checker walks the whole tree rather than reading the first record.
- What is your hard bounce rate? Above roughly two percent and providers read the list as bought or stale.
- What is your complaint rate? Google publishes the number: stay under 0.1 percent and never reach 0.3 percent.
- What is your volume per mailbox? Eight to ten cold sends a day is the figure that holds. A mailbox that jumped to four hundred looks like software regardless of any list.
In our experience those four account for the large majority of "we must be blacklisted" reports.
If you are listed, read the bounce
A real blocklist rejection names itself. You will see something like 550 5.7.1 Service unavailable; Client host [203.0.113.10] blocked using zen.spamhaus.org. That string tells you the list, the identity listed and where to go. If your bounces say something else, such as Google’s 550 5.7.1 ... likely unsolicited mail, you are not blocklisted. You have a reputation verdict from that one provider, which no delisting form will clear.
Getting delisted, and making it stick
Fix the cause before you request removal. Relisting is automatic and usually faster the second time, and repeated cycles make the eventual listing harder to clear.
Spamhaus operates a self service removal for most listings and processes it quickly once the behaviour has stopped. SpamCop expires listings automatically as complaints age out. Barracuda takes a removal request form. None of them require payment, and services that charge to "clean" your reputation are selling you a form you can submit yourself.
The cause is usually one of three things: a compromised account sending without your knowledge, a bought or scraped list producing spam trap hits, or volume that outran the domain’s history. The third is the one cold email teams hit most, and the fix is fewer sends per mailbox across more mailboxes rather than a faster ramp.
Spam traps, briefly
A pristine trap is an address that never belonged to a person and was published only to catch scrapers. A recycled trap is a real address that was abandoned and repurposed. Hitting either is a strong signal, and it is the usual explanation when a list that "looked fine" gets a domain listed within days. Verification catches dead addresses; it does not reliably catch traps, which is the practical argument against buying lists.
Questions, answered straight
- How do I check if my email is blacklisted?
- Look up the sending IP and the sending domain separately. For the IP, check Spamhaus SBL and XBL, SpamCop and Barracuda. For the domain, check Spamhaus DBL and SURBL. A multi-lookup service queries dozens at once, but only a handful of lists meaningfully affect delivery, so read those first and ignore the long tail.
- Which blocklists actually matter?
- Spamhaus is the one that matters most, because the major mailbox providers and a large share of corporate filters consult it. SpamCop and Barracuda affect a narrower set of receivers. Appearing on an obscure list that nobody queries has close to zero effect, which is why a scary looking report showing one hit out of eighty is usually not your problem.
- My mail goes to spam but I am not on any blocklist. Why?
- Because blocklists are a small part of filtering. Gmail and Outlook rely mainly on their own reputation signals: how recipients treat your mail, whether authentication aligns, your complaint rate and your bounce rate. A domain can be clean on every public list and still be filtered, and this is the common case rather than the exception.
- How do I get removed from a blocklist?
- Every list publishes its own delisting form. Fix the cause first, because relisting is automatic and faster the second time. Spamhaus delists quickly once the sending behaviour stops. Self service removal exists on most lists, and paying anyone for a removal service is unnecessary.
- Does being on a blocklist affect my whole domain?
- It depends which identity was listed. An IP listing affects everything sending from that IP, which on shared infrastructure includes other senders. A domain listing follows the domain everywhere, including mail sent through a different provider, so it is the more serious of the two.
Published 20 September 2026. Updated 20 September 2026. Written by the team that runs the infrastructure; numbers come from the platform's own provisioning and sending, and from the providers' published documentation at the time of writing.