If your business email is bouncing, landing in spam, or being rejected by Outlook, Hotmail, or another mail provider, your sending IP address may have a poor reputation or appear on an email blocklist.
The solution is not always to change your mail server or IP address. First identify which blocklist or receiving provider is rejecting your messages, fix the underlying problem, and then follow the correct removal or support process.
This guide explains how to check your sending IP, request removal from the major email blocklists, contact Microsoft about Outlook.com delivery failures, and verify that email delivery has actually recovered.
Start here: check your IP with the free Email Blacklist Checker — it queries 50+ DNSBL sources in one run, including Spamhaus, Barracuda and URIBL.
Quick links: email blacklist removal portals
| Provider | Official removal or support page | When to use it |
|---|---|---|
| Spamhaus | check.spamhaus.org | Your IP or domain is listed in a Spamhaus dataset (CSS, SBL, XBL, PBL, DBL) |
| Microsoft 365 | sender.office.com | Your sending IP is rejected by Microsoft 365 recipients |
| Microsoft Outlook.com Sender Support | olcsupport.office.com | You cannot deliver to Outlook.com, Hotmail, Live or MSN recipients, including repeated S3150 errors |
| Barracuda | barracudacentral.org/rbl/removal-request | Your IP is listed in the Barracuda Reputation Block List (BRBL) |
| SpamEatingMonkey | spameatingmonkey.com/remove | Your IP or domain appears on a SpamEatingMonkey list |
| SpamCop (SCBL) | spamcop.net/bl.shtml | Your IP received user spam reports — the listing is time-based and expires on its own |
| blocklist.de | blocklist.de/en/search.html | Your IP was reported for attacks (SMTP/IMAP/SSH brute force, spam bots), not necessarily for sending spam |
These are separate systems. Removing an IP from one provider's blocklist does not automatically remove it from the others, and it does not guarantee that a receiving provider will start accepting your mail again.
Step 1: Check your sending IP address
Before requesting removal, identify the public IP address that actually sends your outbound email. This is often different from your website server IP, your inbound MX server, or the address shown by a general IP lookup service.
- Find the outbound SMTP server's public IP in your mail server configuration or outbound message logs.
- If a message bounced, inspect the full non-delivery report (NDR) and note the IP mentioned in the rejection.
- Enter that IP into the Email Blacklist Checker.
- Review which lists report a listing, then follow that provider's official removal process below.
A clean result on one blocklist does not mean your IP is trusted everywhere. Several providers run private reputation systems, and some will keep rejecting mail after a public listing has been removed.
If you are unsure which hostname resolves to which address, use the PTR lookup tool to confirm the reverse DNS name behind the sending IP before you contact anyone.
Step 2: Fix the cause before requesting removal
A delisting request is not a substitute for fixing the mail server. If your server keeps sending unwanted or unauthorized messages, your IP will be listed again after removal.
Review these areas before you submit anything:
- Compromised accounts: look for stolen credentials, suspicious logins, abused mailboxes and unauthorized SMTP authentication.
- Outbound mail logs: check for unusual volume, repeated recipients, unexpected sending accounts or unexplained spikes.
- SMTP security: disable open relaying and restrict who can send through your mail server.
- SPF: confirm the sending IP is authorized by the domain's SPF record with the SPF checker.
- DKIM: make sure outbound messages are signed and the signature validates with the DKIM checker.
- DMARC: publish an appropriate policy and review alignment with the DMARC checker.
- Reverse DNS (PTR): confirm the sending IP has a matching reverse DNS record.
- HELO/EHLO: use a valid, resolvable hostname consistent with your mail server configuration.
- Recipient quality: stop sending to invalid, outdated or unconsented addresses, and stop retrying failing recipients.
You may need your hosting provider or network operator if you do not control the PTR record for the sending IP.
Step 3: Request removal from Spamhaus
Official portal: check.spamhaus.org
Spamhaus operates several datasets, including CSS, SBL, XBL, PBL and DBL. The correct remediation process depends on which dataset contains the listing.
- Open the official Spamhaus IP and Domain Reputation Checker.
- Search for your sending IP address or the affected domain.
- Open the listing details and read the explanation.
- Fix the underlying problem before requesting removal.
- Follow the removal instructions shown for that specific listing.
- Explain what caused the problem, what you changed, when you fixed it, and how you will prevent a recurrence.
- Save the request or ticket details and check the listing again later.
Spamhaus requires enough information about the cause and the remediation. Repeated requests without fixing the issue are ineffective and may lead to additional restrictions.
SBL is handled differently from CSS. For an SBL listing, the responsible internet service provider generally has to submit the removal request. Follow the instructions displayed for your specific listing rather than reusing a CSS template.
Spamhaus removal request template
Use the following as a starting point and replace every placeholder with verified facts.
Subject: Request for Removal - [YOUR SENDING IP]
Dear Spamhaus Team,
We are requesting a review of the listing for [YOUR SENDING IP] / [YOUR DOMAIN].
We identified [ACTUAL CAUSE OF THE LISTING] and took corrective action on
[DATE AND TIME, INCLUDING TIME ZONE].
The actions taken include:
- [Account, server or configuration issue that was corrected]
- [Security measures implemented]
- [How outbound email activity is now monitored]
We have reviewed our outbound mail logs and are monitoring the server to
prevent a recurrence.
Please review the current listing and advise whether the IP address or
domain is eligible for removal.
Thank you for your assistance.
Best regards,
[Your Name / Organization]Do not claim an issue has been resolved unless you have verified it. Inaccurate remediation statements are a common reason requests are denied.
What happens after a Spamhaus removal
A successful removal does not guarantee that every receiving network updates immediately. Spamhaus notes that many networks catch up within one to two hours, although some synchronization problems take longer.
If mail keeps failing, read the rejection message. If only one receiving provider still rejects your mail, contact that provider instead of submitting the same Spamhaus request again.
Step 4: Resolve Microsoft Outlook and Hotmail delivery errors
Official links: Microsoft IP delisting portal · Outlook.com Sender Support · Microsoft sender guidance
Microsoft runs its own filtering and reputation systems. A clean Spamhaus result does not mean Microsoft will accept your mail: Outlook.com and Microsoft 365 can reject an IP that no public blocklist lists at all.
What does error S3150 mean?
A common rejection looks like this:
550 5.7.1 Unfortunately, messages from [YOUR_IP] weren't sent ... (S3150)This indicates that Microsoft's receiving system is rejecting the sending IP under its filtering or reputation controls. It does not, on its own, prove that Spamhaus still lists the IP.
How to request Microsoft IP delisting
- Open the Microsoft IP delisting portal at sender.office.com.
- Enter a working contact email address and the sending IP identified in the rejection.
- Complete the verification process.
- Follow the portal's instructions and keep the response.
- If Outlook.com or Hotmail still rejects mail, submit a case through Outlook.com Sender Support.
- Include the full rejection text, sending IP, timestamp and corrective actions.
Use the IP address explicitly named in the rejection message. Do not assume the website IP or the inbound MX address is the one being blocked.
What to include in an Outlook.com support request
- Sending IP address.
- Sender domain.
- Full SMTP rejection or non-delivery report.
- Date and time of the failure, including time zone.
- Existing support request number, if one exists.
- Confirmation of the corrective actions you performed.
- Current status of any relevant public blocklist listings.
If Microsoft has already opened a case or sent a mitigation response, reply to that existing email thread with the newest rejection and keep the original subject line unchanged.
What does conditional mitigation mean?
Microsoft may grant conditional mitigation instead of restoring full sending reputation immediately. A mitigation notice can state that the IP is unblocked but subject to low daily sending limits until it establishes a good reputation, and that further complaints can withdraw the mitigation.
Follow the exact terms in your own support response. If Microsoft specifies a 24-48 hour propagation period, allow that period to pass before concluding the change failed. This is a stated propagation window, not a guarantee that every message will be accepted.
What if the same S3150 error continues?
- Check the timestamp of the latest rejection.
- Confirm whether the stated mitigation period has elapsed.
- Stop sending repeated test messages and stop filing duplicate delisting requests.
- Reply to the existing support case with the newest rejection and timestamp.
- Ask Microsoft to verify whether the mitigation propagated, or whether the IP is still blocked by its reputation systems.
A successful delisting request does not guarantee inbox placement. Microsoft can still filter messages based on sending behavior, authentication, complaint rates, content and other reputation signals.
Step 5: Request removal from Barracuda
Official removal page: barracudacentral.org/rbl/removal-request
Barracuda operates its own reputation system. A clean Spamhaus result does not clear a Barracuda listing.
- Open the official removal request page.
- Enter the email server IP address.
- Enter a contact email address you can actually access.
- Provide a phone number.
- Fill in Barracuda customer information if the form requires it.
- Explain the cause of the issue and the remediation you performed.
- Submit the request once and keep the result.
Barracuda states that requests with a valid explanation are typically investigated and processed within 12 hours. That is an estimate, not a service level, and duplicate requests may be ignored.
Barracuda removal request template
Dear Barracuda Reputation Team,
We are requesting a review of the IP address [YOUR SENDING IP] in the
Barracuda Reputation System.
We identified [ACTUAL CAUSE] and stopped the associated activity on
[DATE AND TIME, INCLUDING TIME ZONE].
We have reviewed our mail server logs and implemented the following
corrective actions:
- [Issue fixed]
- [Security changes made]
- [Ongoing monitoring in place]
We kindly request a review of the current IP reputation and removal of the
listing if the issue has been resolved.
Sending IP: [YOUR SENDING IP]
Mail domain: [YOUR DOMAIN]
Thank you for your assistance.
Best regards,
[Your Name / Organization]Step 6: Request removal from SpamEatingMonkey
Official request page: spameatingmonkey.com/remove
SpamEatingMonkey maintains its own lists. Confirm the exact list and listing type before requesting removal.
- Open the removal page.
- Confirm that the IP address or domain shown is the resource you want reviewed.
- Explain the actual cause and your corrective actions in the justification field.
- Provide a working contact email if you want a reply.
- Submit the request and keep any confirmation.
If a domain is listed because of URLs found in spam messages, remediation has to focus on compromised pages, injected links or abused redirects — not only on the sending IP.
SpamCop and blocklist.de: report-driven lists that expire
These two lists behave differently from the providers above, and that changes what "removal" means.
SpamCop Blocking List (SCBL)
SpamCop is time-based: an IP is listed because SpamCop users reported mail coming from it, and the entry expires automatically once reports stop. There is no negotiated appeal process that restores an IP while it keeps generating complaints.
- Check the status at spamcop.net/bl.shtml.
- Find what is still being reported — a compromised mailbox, a stale recipient list, or a form that emails user-supplied content.
- Stop the traffic. The listing then ages out on its own, usually within a day or two of the last report.
- Do not restart the same campaign at full volume to "test" whether the listing cleared.
Because SCBL is aggressive by design, a listing can also come from a single complaint. Check the report links if you received a SpamCop report, and treat repeated listings as a signal that the underlying sending behavior never changed.
blocklist.de
blocklist.de is not a spam list in the usual sense. Its data comes from Fail2Ban-style reports (X-ARF) submitted by server operators for attacks on SSH, SMTP/IMAP authentication, FTP, web applications and spam bots.
- Look the IP up at blocklist.de/en/search.html to see the reported attack type.
- An SMTP or SASL entry usually means an account is being password-sprayed or a mailbox credential leaked — rotate credentials and enable MFA.
- If you are mid-remediation, blocklist.de lets the abuse contact pause reports for that IP for seven days while you fix the host.
- Being on this list does not mean your mail content was reported as spam, so do not "fix" content when the logs show authentication failures.
Neither list takes a paid removal, and neither is cleared by a template request. Fixed behavior is the removal mechanism.
Generate your removal request
Pick the provider that is actually blocking you, describe only what you verified, and copy the request into their official form or support thread.
Removal request builder
Fill in what you actually verified and copy a ready-to-send English request. Blank fields stay as placeholders — nothing is submitted anywhere by this page.
Subject: Request for Removal - [YOUR SENDING IP] Dear Spamhaus Team, We are requesting a review of the listing for [YOUR SENDING IP] / [YOUR DOMAIN]. We identified [ACTUAL CAUSE OF THE LISTING] and took corrective action on [DATE AND TIME, INCLUDING TIME ZONE]. The actions taken include: - [Describe the account, server or configuration issue that was corrected] We have reviewed our outbound mail logs and are monitoring the server to prevent a recurrence. Please review the current listing and advise whether the IP address or domain is eligible for removal. Thank you for your assistance. Best regards, [Your Name / Organization]
Submit through the Reputation Checker page for the specific listing (CSS, SBL, XBL, PBL or DBL). SBL requests normally have to come from the ISP that owns the IP. Read the full Spamhaus process.
Never claim a fix you have not verified. Blocklist operators reject requests that contain inaccurate remediation details, and a delisting request never guarantees inbox placement.
Step 7: Verify that email delivery has recovered
Do not stop when a removal request is accepted. Verify the outcome systematically.
- The original blocklist no longer reports the listing.
- The receiving provider no longer returns the same blocklist-related error.
- SPF passes for the actual sending IP.
- DKIM signatures validate.
- DMARC alignment is correct for the visible From domain.
- PTR and HELO/EHLO settings are valid.
- Outbound mail logs show no continuing unauthorized activity.
- A small number of legitimate business messages are delivered.
- Messages are not consistently landing in spam folders.
- Monitoring is in place to detect new listings or failures.
Send only to known, consenting recipients when testing. Avoid large batches, repeated retries and unverified addresses.
A message accepted by a receiving server is not necessarily delivered to the inbox. Acceptance, inbox placement and long-term reputation are three different outcomes — use the deliverability test and header analyzer to see which one you are actually getting.