Check blocklists and your email sending reputation

The short version

• Read the bounce first. It often names the list or the reason, and gives a removal link.
• Find your sending IP. It’s in the headers of a message you sent, or in the bounce.
• Spamhaus: look up the IP and your domain at check.spamhaus.org. It’s free.
• Microsoft 365 recipients: if the bounce says “banned sending IP,” use the delist portal at sender.office.com.
• Gmail: add your domain to Postmaster Tools to see spam rate, authentication and compliance status.
• Fix the cause before you ask for removal, or you’ll be listed again.

How do I check, step by step?

1. Read the bounce

If you have a bounce (also called a non-delivery report), it’s your best clue. Look for a code starting with 5 and any link it includes. Our help page on bounced email explains the common codes. A few to know:

• Microsoft 365, 550 5.7.606 to 5.7.649 “Access denied, banned sending IP”: your server’s IP is on Microsoft’s blocked senders list. Microsoft’s delist page has the steps.
• Microsoft 365, 550 5.7.511 “banned sender”: you can’t self-delist. Microsoft says to forward the bounce to delist@microsoft.com.
• Outlook.com, 550 5.7.515: your domain doesn’t meet the authentication rules for high-volume senders; see the bulk-sender rules.
• Gmail: its rejections include a code naming the failing requirement, such as SPF or DKIM.

2. Find your sending IP address

If you use Microsoft 365 or Google Workspace, you share their sending servers, and they manage those addresses’ reputation. Blocklisting is far more likely for:

• your web server, if the website sends mail directly;
• an office mail server or older hosted mail server;
• a scanner or app sending through your own server.

The safest way is to look at the receiving side. Send a message from the affected mailbox or form to a personal Gmail address, open it, choose Show original, and find the Received-SPF line. The address after client-ip= is the server that handed your message to Google, and that’s the one to check. Lower Received: lines often show your own computer or an internal address, such as one starting 192.168 or 10., and those aren’t the ones to look up.

3. Look it up at Spamhaus

Spamhaus’s IP and Domain Reputation Checker, at check.spamhaus.org, takes an IP address, domain or email address. It shows which Spamhaus list has you, why, and what to do. Check your domain too, not just the IP. Spamhaus explains the order: an SBL listing has to be handled first, through your internet or hosting provider. The PBL lists home and dynamic addresses, and being on it is normal unless you run a mail server there.

4. Check Microsoft’s lists

If mail to Microsoft 365 addresses bounces with a banned-IP code:

1. Go to the Office 365 Anti-Spam IP Delist Portal at sender.office.com.
2. Enter the email address that received the bounce and the IP address from the error.
3. Select Submit, then the confirmation link Microsoft emails you.
4. Select Delist IP.

Microsoft says it can take up to 24 hours or longer. For consumer Outlook.com addresses, Microsoft points to a separate support form. If you run your own sending server, Microsoft’s SNDS shows how Outlook.com sees your IP addresses.

5. Check Gmail with Postmaster Tools

Postmaster Tools is Google’s free dashboard for senders. After you verify your domain, its dashboards show a Compliance status against Gmail’s sender rules, your spam rate, and how much of your mail passes SPF, DKIM and DMARC. Google says data is usually updated within 24 hours, and the compliance status can take up to 7 days to reflect a fix.

Why does it matter?

A listing can stop your mail at many companies at once, because spam filters everywhere use the big blocklists. It’s also a warning sign. A listed web server often means a hacked site or a contact form being abused to send spam. Fixing the listing without fixing that just buys a few days.

What are the common mistakes?

• Requesting removal before fixing the cause. You’ll be relisted, and some lists slow down repeat requests.
• Paying for “guaranteed delisting.” The major lists offer removal free.
• Panicking about obscure lists. Many free checkers show dozens of lists, some of which almost no one uses. Focus on what your bounces name and on Spamhaus, Microsoft and Gmail.
• Checking only the IP. Domain-based lists exist too.
• Ignoring a hacked website. If your web server is listed, see what to do if your site was hacked.

What if I’m not listed but mail still goes to spam?

Then the problem is usually authentication or content. Check SPF, DKIM and DMARC with our email deliverability checker, look for failing senders in your DMARC reports, and make sure website mail goes through an authenticated service, as in making your website send email properly. Our answer on why emails go to spam covers the rest.

How much does it cost, and how long does it take?

The lookups and delisting requests above are free. A check takes a few minutes. Removal takes anywhere from minutes to a few days, depending on the list. Fixing the cause, like cleaning a hacked site or moving form mail to a proper service, is usually the longer job.

How does E-3 handle this?

When a client’s mail bounces, we usually start with the full bounce code, then look at the domain’s records and whether anything changed recently in DNS or hosting. If a server is listed, we look for the cause before asking for removal.

Related questions

• Why can’t I send email, or why do my messages bounce?
• Why are good emails landing in my junk folder?
• Do the bulk-sender rules apply to me?
• What should I do if my site was hacked?
• Back to the complete guide to business email that lands

Sources

1. Goodbye Blocklist Removal Center, hello IP and Domain Reputation Checker (Spamhaus)
2. Remove yourself from the blocked senders list (Microsoft Learn)
3. Smart Network Data Services (Microsoft Outlook.com)
4. Postmaster Tools dashboards (Gmail Help)
5. Email sender guidelines FAQ (Google Workspace Admin Help)