Email Blacklist: Check, Causes, Removal

What is an email blacklist?

An email blacklist, now usually called a blocklist, is a database of IP addresses or domains that an operator has seen sending spam. Most of these lists are published over DNS, which is why they're called DNSBLs. When a server connects to deliver mail, the receiving server reverses the order of the octets in that IP address. It then adds the list's zone, for example zen.spamhaus.org, and runs a DNS lookup on the result. If an address record comes back, the IP is listed. If nothing comes back, it isn't. Domain lists work the same way, except they look up the domain name itself. That domain can come from your envelope sender, your From header or the links in the message body.

The list operator doesn't block anything itself. The receiving server decides whether to reject the message, send it to spam or just add points to its spam score. That's why one listing can hurt at one mailbox provider and do nothing at another. A rejection caused by a list usually comes back as a permanent failure that says delivery wasn't authorised, and the error text often names the list. Our guide to email bounce codes and their causes shows how to read that line in a bounce notice.

Which email blacklists actually matter?

There are a great many public lists, and online checkers query dozens of them at once. In practice, a handful of widely used lists cause most rejections. The rest are niche, or few receiving servers query them. The main split is between lists of sending IPs and lists of domains, because each type has different triggers and a different removal process.

List	What it lists	Typical trigger	How removal works
Spamhaus ZEN (SBL, XBL, PBL)	Sending IPs	Spam sources, infected machines, IP ranges not meant to send mail directly	Lookup and removal request on Spamhaus's own website, once the cause is fixed
Spamhaus DBL	Domains	Domains seen in spam, as the sender or in links	Removal request through Spamhaus once the cause is fixed
Barracuda BRBL	Sending IPs	Mail that hits Barracuda's own traps and filters	Removal request form on Barracuda's site
SpamCop SCBL	Sending IPs	Spam reports submitted by users	SpamCop's own FAQ says entries expire on their own once the reports stop
SURBL	Domains found in message bodies	Links in your mail that point to listed domains	Lookup and removal request on SURBL's site

If you send through a shared IP pool at your email provider, an IP listing may have been caused by other senders on that pool. Your provider deals with those. A domain listing is different. Only you send with your domain, so the cause is on your side.

How do I check if my email is blacklisted?

First, find the IP that actually delivered your mail. Send a message to a test inbox, open the original source and read the first Received header that the recipient's server wrote. Then check that IP and your sending domain in one of these ways:

• Multi-list checker: MXToolbox's blacklist check and MultiRBL each run one IP or domain against many DNSBLs at once. They're good for a quick overview. Keep in mind that a hit on an obscure list may have no effect at all.
• The operator's own lookup: Spamhaus, Barracuda and Abusix each offer a lookup page for their own data. Use these before you ask for removal, because they usually explain why you were listed.
• Command line: run dig +short on your reversed IP followed by the list's zone, for example zen.spamhaus.org. If an address comes back, you're listed. An empty answer means you're not.
• Watch which DNS resolver you use: Spamhaus's documentation says it refuses queries that come through large public resolvers such as Google Public DNS or Cloudflare. Instead of a real answer, those queries get an error code, which can look like a listing. Use your own resolver or your ISP's, or use the operator's web lookup.

A clean blocklist result doesn't mean your mail reaches the inbox. Gmail and Microsoft rely mostly on their own reputation data. For those providers, Google Postmaster Tools and the steps in our article on checking and fixing sender reputation tell you more. Check SPF, DKIM and DMARC at the same time with the SPF, DKIM and DMARC checker, because a broken record and a listing often turn up together. The overview of deliverability tools sorted by job names more tools for each task.

Why do cold email senders get blacklisted?

List operators work from evidence: their own trap addresses, spam reports from users, and network data. In B2B outreach, almost every listing comes down to one of these causes:

• Pristine spam traps: addresses that never belonged to a real person and were placed where scrapers would find them. Mail to one of them shows the address was harvested rather than collected.
• Recycled spam traps: abandoned addresses that a provider has turned into traps. Old or bought lists reach them because nobody checked whether the contact still exists.
• Spam complaints: recipients clicking 'report spam'. SpamCop builds its list from exactly these reports.
• Lots of hard bounces: a large volume of mail to addresses that don't exist looks like someone guessing addresses. It often happens when people send to unverified catch-all domains.
• Hijacked accounts or forms: a compromised mailbox or an unprotected web form sending spam from your IP or domain.
• Links to a listed domain: if a URL shortener or tracking domain in your message is listed on SURBL or the Spamhaus DBL, it drags your message down with it.

Fixing your DNS records won't get you off a list by itself. SPF, DKIM and DMARC prove who sent a message. They don't change whether that message hit a trap. Volume matters too: a sudden jump in sending from a fresh domain is something operators notice. Our article on how many cold emails per day per mailbox covers that.

How to get removed from an email blacklist

1. 1 Stop sending from the affected IP or domain. Every message that keeps hitting traps renews the listing.
2. 2 Read the reason on the operator's lookup page. Spamhaus, Barracuda and the others usually say what kind of evidence led to the listing.
3. 3 Fix the cause. Remove bought or old contacts, delete hard bounces, secure compromised accounts and forms, and take out links to listed domains.
4. 4 Check your authentication. SPF and DKIM should pass, you should have a DMARC record at _dmarc, and both checks should align with your From domain.
5. 5 Submit one removal request through the operator's own form. Don't pay anyone who offers delisting for a fee. The major lists don't sell removal.
6. 6 Start sending again slowly with a cleaned list, and check the lists again after a few days.

Here's what doesn't work. Switching to a new domain while keeping the same list fails because the new domain hits the same traps and gets listed for the same reason. Sending repeated removal requests before you've fixed anything fails too, and some operators make the next removal harder after that. If mail still lands in spam after you've been delisted, work through why your emails are going to spam. The blocklist was only one of several signals.

Sales follow up emails without risking a listing

Follow-ups count toward your sending volume, and they go to the same list as the first email. If the list is the problem, every follow-up repeats it. Each point below stands on its own:

• Sales follow up email template: keep it short. Mention the first email in one line, give one new reason to reply, and end with one question. Send it as a reply in the same thread so the In-Reply-To header links the two, and include a way to unsubscribe.
• Follow up sales email: send it only to addresses that didn't bounce the first time. A follow-up to an address that hard-bounced is a second strike against an address that doesn't exist.
• Cold email deliverability: the receiving server decides it based on authentication, domain and IP reputation, complaints, bounces and volume. A blocklist hit is one of those inputs, so a clean blocklist check doesn't mean you'll reach the inbox.
• Sales email follow up templates: changing the wording is fine, but filters weigh reputation and complaints more than phrasing. No template makes up for a list that contains spam traps.
• Sales follow up email: stop after a clear 'no', an unsubscribe or a complaint. Sending more after a complaint leads straight onto SpamCop's report-based list.
• Sales follow up email examples: for instance, 'Hi Anna, quick follow-up on my note from Tuesday about onboarding for your new hires. Would a short call next week be useful, or is this not a priority right now?'

The full set of templates for no-reply, post-call and breakup emails is in the sales follow up email template collection.

How EmailFlow OS sends: your Brevo account, your domain

EmailFlow OS is built for senders who want to keep control of their own reputation. You record one video and upload it to EmailFlow OS. You connect your own Brevo account and sending domain, and you import your prospect list into EmailFlow OS. EmailFlow OS then creates a personalised version of that one recording for each recipient, not for each company. Every version goes out from your own inbox, through your Brevo account and your domain. Nothing is sent from a shared platform sender.

For blocklists, that has two consequences. A domain listing reflects your list and your sending, not other customers'. And list quality is your job. Because the prospect list lives in EmailFlow OS, that's where you remove old, bought or bounced contacts before a send. EmailFlow OS can't decide whether a receiving server accepts a message, and a clean list doesn't guarantee you'll stay off every blocklist. The EmailFlow OS personalised AI video email page has more on the setup.

Questions people ask

? What is the difference between a blacklist and a blocklist?

Technically there's none. Both words mean a DNS-based list (a DNSBL) that receiving servers look up for a sending IP or domain. Operators such as Spamhaus now say 'blocklist'. The difference that matters is between IP lists like Spamhaus ZEN and domain lists like the Spamhaus DBL or SURBL. They're triggered differently and cleared differently.

? How long does an email blacklist listing last?

It depends on the list. SpamCop's FAQ says its entries expire on their own once the reports stop. Spamhaus and Barracuda remove a listing after you fix the cause and request removal on their own sites. If you ask for removal without fixing the cause, the next trap hit can put you straight back on the list.

? Does being on one blacklist block all my email?

No. Each receiving server chooses which lists it queries and what it does with a hit: reject the message, move it to spam or add to its spam score. A listing on a widely used list like Spamhaus ZEN affects many receivers. A listing on an obscure list that few servers query may have no visible effect.

? Can I check a blacklist through Google Public DNS?

Not reliably for Spamhaus. Its documentation says it refuses queries that come through large public resolvers such as Google Public DNS and Cloudflare, and sends back an error code instead of a real answer. That error can look like a listing. Use your own resolver or your ISP's, or Spamhaus's web lookup, to get a correct result.