Why Am I Blacklisted, and How Do I Get Off an Email Blacklist?

Your email is blacklisted because a spam-monitoring service saw spam, or something that looked like spam, coming from your domain or your mail server’s IP address, and added it to a list that receiving mail servers consult before accepting a message. Nobody sends you a notice; you find out when messages bounce or quietly stop arriving. Getting off the list means finding what sent the spam, fixing it, and then asking each list to remove you. This article, first published in 2013 and updated in September 2026, explains how blacklists work, what puts a business on one, and how to get off and stay off.

How blacklists work

Blacklists, also called blocklists or DNSBLs, are databases of IP addresses and domains that have recently sent spam, hosted malware or been misconfigured in ways spammers exploit. When a mail server receives a message it checks the sender against one or more lists and rejects, delays or junks the mail accordingly. The lists that matter most are Spamhaus, whose lists nearly every mail provider uses, and the reputation systems inside Microsoft and Google, which decide whether Outlook.com, Microsoft 365 and Gmail users see your message. SpamCop, SORBS, Barracuda and UCEPROTECT are among the many others. Being on a minor list is an annoyance; being on Spamhaus or in Microsoft’s block list stops most of your outbound email.

What gets a business listed

• A compromised mailbox. The most common cause. A phished password lets an attacker send thousands of spam or phishing messages from a real employee’s account, and the domain’s reputation collapses within hours.
• An infected computer. Malware that sends spam in the background through your connection gets the office’s public IP listed, which affects every device behind it.
• Bulk sending from a business mailbox. A newsletter to two thousand contacts from Outlook looks exactly like spam to the receiving servers, and complaints from a few recipients are enough.
• Missing authentication. No SPF record, no DKIM signing, no DMARC policy, or a mismatch between them. Without these, receiving servers cannot tell your mail from a forgery, and forgers using your domain damage your reputation.
• Configuration problems. No reverse DNS record for the mail server, an open relay, or a web contact form that lets anyone send mail through your server.
• Shared reputation. A shared hosting IP, or a bad neighbour on the same range, can carry your domain along with it.

How to check

Look up the mail server’s IP and the domain on a multi-list checker such as MXToolbox, then check Spamhaus directly. Read a recent bounce message: it usually names the list that rejected the mail and gives a link. For Microsoft and Google reputation, register the domain with Microsoft SNDS and Google Postmaster Tools, which show complaint rates and reputation over time. Our free email spoofing check tests whether your SPF, DKIM and DMARC are set up so that your domain cannot be impersonated.

How to get delisted

1. Find the cause. Check the mail server’s outbound logs and the sent items of every mailbox for messages nobody sent. Look for mailbox forwarding rules an attacker may have added. Scan computers for malware. Close open relays and abused forms.
2. Fix it. Reset the compromised password and turn on multi-factor authentication, remove the malware, publish or correct SPF, DKIM and DMARC, add the reverse DNS record. A delisting request while spam is still flowing is refused and makes the next request harder.
3. Request removal from each list. Every list has a removal form. Spamhaus removes fixed senders quickly; some smaller lists expire automatically after a period without new spam; Microsoft and Google recover reputation gradually as clean mail flows.
4. Warn recipients if needed. If the compromise sent phishing to your customers, tell them, briefly and honestly, so they do not click.

Staying off

Multi-factor authentication on every mailbox, so a stolen password alone cannot send. Email security filtering, $6 per mailbox per month on our published rates, which also stops a compromised account from sending in bulk. SPF, DKIM and DMARC published and monitored. A proper marketing platform for newsletters, never a business mailbox. Endpoint protection on every computer. And someone watching the sign-in logs, which is what a managed plan provides. Our guide to reducing spam covers the inbound side of the same problem, and if your mail server is on site, we can audit its configuration.

Common questions

How do I check whether we are blacklisted?

Look up your mail server’s IP address and your domain on a multi-list checker such as MXToolbox, and directly at Spamhaus, which is the list that matters most. Bounce messages also usually name the list that rejected the mail. Microsoft and Google have their own reputation systems, visible through Microsoft SNDS and Google Postmaster Tools.

Why was our email server blacklisted?

Almost always because something sent spam from your address or your IP: a compromised mailbox, an infected computer, a web form being abused, or a bulk marketing send from a business mailbox. Misconfiguration, such as a missing reverse DNS record or an open relay, is the other common cause.

How do we get off a blacklist?

Find and fix the cause first, because a delisting request while spam is still flowing is refused and makes the next one harder. Then request removal from each list through its website. Most remove a fixed sender within a day or two; some expire automatically after a period without new spam.

Does a blacklist affect Microsoft 365 or Google Workspace mail?

Your domain can still be blocked or sent to junk if it is spoofed or if a mailbox is compromised, even though the sending servers belong to Microsoft or Google. Domain reputation and SPF, DKIM and DMARC are what protect you there.

How do we stay off blacklists?

Multi-factor authentication on every mailbox, filtering that stops a compromised account from sending in bulk, SPF, DKIM and DMARC published correctly, a separate marketing platform for newsletters, and endpoint protection so an infected computer cannot send spam quietly in the background.

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