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Email blacklisted? How to check and get removed

If bounces mention Spamhaus, a blocklist or "S3150", your domain or sending IP has been listed. Here's how to find out which, fix why it happened, and ask to be removed.

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First: is it your domain or your IP?

Blacklists, also called blocklists, list two different things, and it matters which one you're on:

Your sending IP address, the server your mail leaves from. If you use Google Workspace, Microsoft 365 or another big provider, you share their IPs, and a listing there is their problem to fix, not yours.
Your domain, such as yourcompany.com. A domain listing follows you whatever provider you use, so it's always yours to fix.

Read the bounce message carefully. It usually names the list and what was listed. Then check your domain and your sending IP with a blacklist lookup. Spamhaus has its own free reputation checker on its website, which tells you which list you're on and whether you can request removal.

Fix the cause before you ask

Every list will relist you, often faster the second time, if the problem is still there. Spamhaus can also take away self-service removal until it's satisfied the issue is fixed. Common causes for a small business:

A hacked mailbox sending spam. Change the password, turn on two-factor sign-in, remove unknown forwarding rules, and check your provider's sign-in log.
A compromised website or contact form sending spam, or hosting a phishing page. Clean the site and update everything.
A bought or old mailing list that hit spam traps: addresses that exist only to catch senders who don't get permission.
Your own server left open as a relay, or with no reverse DNS.

How to get off Spamhaus

Look up your IP or domain in Spamhaus's reputation checker.
Read the listing reason it gives.
Fix the cause, then use the removal option the checker offers.
Track the request through Spamhaus's own ticket status rather than opening new tickets.

Some listings expire on their own once the problem stops. Others need a request. A brand-new domain with no history may show poor reputation for a while; that improves with normal, wanted sending.

How to get off Microsoft's blocklist (S3150)

Microsoft keeps its own lists. If mail to Outlook or Microsoft 365 customers bounces with a code like S3150 or 5.7.606 to 5.7.649, the bounce usually points to Microsoft's delist portal at sender.office.com. Enter the blocked IP there and follow the steps. Bounces from Outlook.com and Hotmail consumer addresses may point you to a separate Outlook.com sender support form instead. Always follow the link in the bounce itself.

Other lists

There are dozens of smaller blocklists, and many have little effect on whether mail is delivered. Focus on the ones named in your actual bounce messages. Paid "express delisting" offers from list operators you've never heard of are best ignored.

After you're removed

Make sure SPF, DKIM and DMARC are all in place, so nobody can easily send as your domain and get you listed again. Run the free check to see where you stand.

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Questions

How do I know if my email is blacklisted?

Your bounce messages usually say so, naming the list. To check directly, look up your domain and your sending server's IP in a blacklist lookup tool, or in Spamhaus's own reputation checker for Spamhaus lists.

How do I get removed from Spamhaus?

Look up your IP or domain in Spamhaus's reputation checker, read the listing reason, fix the cause, then use the removal option it offers. If the cause isn't fixed, you'll likely be listed again, and Spamhaus can withdraw self-service removal.

How do I get removed from Microsoft's S3150 block list?

Use the link in the bounce message. For Microsoft 365 and Outlook blocks it's usually the delist portal at sender.office.com, where you enter the blocked IP and follow the steps. Outlook.com and Hotmail consumer blocks may use a separate sender support form.

I use Google Workspace. Is the blacklisted IP my problem?

Usually not. Google Workspace and Microsoft 365 send from shared IPs that they manage. A listed domain, though, is always yours to fix, wherever your mail is hosted.