In this guide · 8 sections
Short answer
Read the bounce message first: it names the list or IP. Check the IP or domain at check.spamhaus.org, and for Microsoft-hosted recipients use sender.office.com. Fix the cause (hacked account, infected website, bad mailing list) before requesting removal, or you will be listed again.
Which blacklists actually matter?
Online checkers query dozens of lists, and a red result on an obscure one rarely affects your mail. The lists and reputation systems that matter for a Singapore small business are the ones big mailbox providers use.
| List or system | What it lists | Where to check |
|---|---|---|
| Spamhaus SBL, XBL, CSS | IPs sending spam or compromised | check.spamhaus.org |
| Spamhaus PBL | End-user IP ranges that should not send mail directly | check.spamhaus.org |
| Spamhaus DBL | Domains with poor reputation, including hijacked ones | check.spamhaus.org |
| Microsoft blocked senders list | IPs blocked from sending to Microsoft 365 | The bounce message; sender.office.com |
| Gmail reputation | Not a public list; domain and IP reputation and spam rate | Google Postmaster Tools |
Spamhaus explains its lists on its blocklists pages. The Policy Blocklist is the one people misread: it lists home and office broadband IP ranges that should not deliver mail directly. Spamhaus says IPs on it are "not necessarily bad". If you send through Microsoft 365 or Google Workspace, your office IP being on the PBL does not affect your email.
How to check: read the bounce, then look up
Follow this order. It stops you chasing listings that have nothing to do with the problem.
Get the full bounce message
Ask the recipient side or check your own inbox for the non-delivery report. Look for an IP address and words like Spamhaus, banned sending IP, 5.7.606 or 5.7.511.
Identify which IP sent the message
If the IP in the bounce belongs to Microsoft or Google, the issue is your account or domain, not the IP. If it belongs to your web host, newsletter tool or office line, that sender is listed.
Check Spamhaus
Enter the IP or domain at Spamhaus's Reputation Checker. It shows which list, if any, and the steps to request removal.
Check Gmail and Outlook reputation
Use Google Postmaster Tools for your domain's spam rate and reputation with Gmail, and Microsoft's SNDS if you run your own sending IPs.
Check your own accounts
In Microsoft 365, look at the Restricted entities page in the Defender portal. In Google Workspace, check alerts and Email Log Search for unusual outbound volume.
Find and fix the cause before delisting
Delisting without fixing the cause is pointless. Spamhaus's hacked help page says that if hacked pages are found after a domain is delisted, it will quickly be relisted, and that after too many relistings it will stop allowing removals until it is sure the problem is fixed.
| Cause | Sign | Fix |
|---|---|---|
| Hacked mailbox | User restricted from sending; replies to mail they never sent | Reset password, revoke sessions, remove rules, turn on MFA |
| Hacked website or CMS | Domain on the DBL; strange pages or files on the site | Clean infected files, update CMS and plugins, secure the server |
| Infected office PC | Office IP on XBL or CSS | Scan and clean devices; check routers and unknown apps |
| Bad mailing list | High spam complaints, old or bought addresses | Send only to opted-in contacts through a proper email tool |
| Misconfigured server | Your own mail server or relay listed | Fix relay and HELO settings, or move sending to your email provider |
A hacked mailbox is the most common case for small businesses. Microsoft 365 automatically blocks a user who exceeds outbound sending limits and adds them to the Restricted entities page; Microsoft calls this an indicator of a compromised account. Follow our hacked business email guide before unblocking.
How to get delisted
Each list has its own process. Use the official form only; never pay a third party who promises removal.
- Spamhaus: use check.spamhaus.org to look up the IP or domain and open a removal ticket once the cause is fixed. For PBL entries, Spamhaus says end users can request an exclusion if their network's policy allows it.
- Microsoft blocked senders list (bounce 5.7.606 to 5.7.649): go to sender.office.com, enter the email address that received the bounce and the IP from the error, confirm via the email link, then select Delist IP. Microsoft says it may take up to 24 hours or longer.
- Microsoft bounce 5.7.511: the portal won't work. Microsoft's delist guide says to email delist@microsoft.com with the full bounce and IP; it replies within 48 hours.
- Microsoft 365 restricted user (your own account): an admin removes the user in the Defender portal under Email & collaboration > Review > Restricted entities, after securing the account. Microsoft says restrictions usually lift within an hour, at most 24 hours.
- Gmail: there is no public delisting form. Reputation recovers as you send wanted mail with correct authentication and low spam reports. Google asks senders to keep spam rates in Postmaster Tools below 0.10% and never reach 0.30%.
Prevent future listings
Most listings are preventable with basic account and website hygiene.
Monthly prevention checks
If mail to Outlook and Hotmail addresses is the specific problem, our Outlook spam guide covers Microsoft-specific checks.
Do it yourself or get help?
Checking Spamhaus and filing a Microsoft delist request takes minutes. Finding and cleaning the cause, such as a compromised mailbox or infected website, is the harder part, and doing it badly means relisting.
Our Emails Land in Spam Fix (S$249) checks authentication, block lists and reputation, fixes the records, and monitors delivery for 14 days afterwards.
Frequently asked questions
Start with the bounce message, which often names the list. Then look up your domain and sending IP at check.spamhaus.org, Spamhaus's reputation checker. For Gmail delivery, verify your domain in Google Postmaster Tools to see reputation and spam rate. Generic multi-list checkers can flag obscure lists that rarely affect delivery.
Usually not. Spamhaus says the Policy Blocklist lists end-user IP ranges that should not send mail directly, and that those IPs are not necessarily bad. If your staff send through Microsoft 365 or Google Workspace, mail leaves from the provider's servers, not your office IP, so a PBL entry does not affect it.
It varies by list. Microsoft says delisting through sender.office.com may take up to 24 hours or longer, and replies to 5.7.511 cases within 48 hours. Microsoft 365 restricted users are usually unblocked within an hour. Spamhaus handles removals through tickets after the cause is fixed. Relisting is quick if the problem returns.
Do not pay third parties offering paid removal. Spamhaus and Microsoft use free official processes: the Spamhaus checker and ticket system, and Microsoft's delist portal or delist email. Removal depends on fixing the cause, such as a hacked account or website, not on payment or persistence.
Microsoft 365 restricts a user who exceeds outbound sending limits or outbound spam policies. Microsoft treats this as an indicator of a compromised account. Secure the account first by resetting the password, revoking sessions, checking rules and enabling MFA, then an admin can remove the user from the Restricted entities page.