Microsoft blocklists

Microsoft manages its own internal blocklists to reject emails from IP addresses or IP networks. Every IP address that is listed with Spamhaus is automatically included in Microsoft's blocklist. According to current knowledge, Spamhaus is the only external (DNS-based) blocklist that Microsoft uses. All other IP addresses or IP networks are listed by Microsoft on the basis of non-public criteria. The blocklists operated by Microsoft contain a high number of false positives, as Microsoft often lists larger IP networks.

There are two separate blocklists that Microsoft uses for different platforms. One of them is used for emails to,, and addresses, the other blocklist is used for all emails routed to Office365.

If you receive an error message from Microsoft when sending emails from one of our servers, please check the error message to find out which blocklist the IP is on. Please make sure that your server is not sending spam and that your IP is not on a DNS-based blocklist. Also make sure that your emails comply with Microsoft's policies, procedures and guidelines, which can be found on the following website:

You can then follow the instructions to remove your IP from the blocklist.


If an IP address is on the Outlook blocklist, e-mails from this IP address will be rejected with the following error message:

550 5.7.1 Unfortunately, messages from [x.x.x.x.x] weren't sent.

Please contact your Internet service provider since part of their network is on our block list (S3140).
You can also refer your provider to

Here you will find the official form to have your IP addresses or IP network areas removed from the block list:

As soon as you have completed the form, you will receive an automatic reply with confirmation of receipt.

Microsoft Support will then reply to you within 12 hours as to whether the IP address has been removed from the blocklist. Microsoft refers to this as 'mitigated' or 'conditionally mitigated'. If you receive the status "not qualified for mitigation" in the e-mail, your IP address has not been removed from the blocklist.

Please note that this email is an automated process from Microsoft. This decision is made by a computer. If the IP address has not been removed from the blocklist, please reply to the e-mail and ask Microsoft for the reason and a new check. Your e-mail will then be escalated and processed manually by an employee. As a rule, the corresponding IP address is then manually removed from the blocklist.

If your request is rejected and the IP address has only recently been assigned to you, please inform Microsoft Support. Microsoft will request an e-mail confirmation or a PDF document from us. To request this confirmation from us, please contact our support by opening a support ticket via our Customer Center and let us know in detail what information Microsoft requires.

In the rare cases where all of the above fails, we can fill out the delisting form for your IP. We do not have specific contacts at Microsoft, but their support sometimes responds differently to a new delisting request. If this does not work, we can change the IP as a last resort.


If the IP address is on the Office365 blocklist, you will receive the following error message:

550 5.7.606 Access denied, banned sending IP [x.x.x.x].
To request removal from this list please visit and follow the directions.
For more information please go to (AS16012609)

To have your IP address or IP network ranges removed from the blocklist, please use the form linked in the error message:

The error message also contains a link to the workflow to have the IP removed from the blocklist:

If you follow these instructions, your IP should be removed automatically.

Recently a second error message was reported for Office365:

550 5.7.511 Access denied, banned sender[x.x.x.x]. To request removal from this
list please forward this message to For more information
please go to AS(1410)

If you contact the above e-mail address, the reply will either ask you to complete the Office365 removal form or forward a recent error message:

Please ensure that you have resolved any issues generating malicious or abusive traffic from
the IP in question and utilize the portal found at
<> to complete the process of IP removal.

Then please wait for 1-2-hour delay before this change propagates through our entire system.
After waiting of 1-2 hour try to send email again.

If you continue to receive Non-Delivery Receipts (NDRs), or "bounce messages," that indicate
that the IP address is still blocked by our spam filtering system, please forward one of the most
recent and complete error message to us and we will investigate further.

In the rare cases where Microsoft still does not remove the IP address, you can contact our support team. Please send us a support ticket via our Customer Center. Please note that we do not have any special contacts with Microsoft either. We can also only complete the IP address removal form. If this still does not produce the desired result, we can assign a new IP address as a last resort.

Microsoft programs

Experienced users may find two free programs from Microsoft for Outlook (not for Office365) helpful: Smart Network Data Services (SNDS) and Junk Email Reporting Program (JMRP).

Please note that you cannot remove your IP from the blacklist via SNDS or JMRP; you will only be offered the following services:

  • Insight into the traffic of the sender IP
  • The reputation of the sender IP at Microsoft and the number of user complaints.

According to Microsoft, there is no magic formula for maintaining or improving a good IP reputation, but with these programs you can optimize your email eco-system to improve deliverability to Microsoft users.


This program allows you to monitor the "health" and reputation of your registered IPs. It provides data about your traffic, such as the volume of emails and the number of user complaints. This data is only provided for IPs that send more than 100 emails per day to Microsoft accounts.

To log in, please visit:

You will need to request authorization for the IPs you wish to access. Microsoft uses a combination of WHOIS and rDNS to determine the owner of a particular IP. In some cases, it is sufficient to send an e-mail to your own domain to verify ownership.

Otherwise, please send a verification request to one of the following e-mail addresses:

We can only verify the registration if the name in SNDS matches the name in the customer center address.


This is similar to a feedback loop (FBL) in that it sends you a copy of an email that has been marked as "junk" by the recipient. However, to prevent listwashing, the JMRP only sends a copy of about 1 in 1000 emails marked as junk. This limits the usefulness of JMRP and means that many senders receive little to no complaints about JMRP, even though recipients actually mark their emails as junk.

You must first be authorized for the IP in SNDS (see above) before you can create a feed for it in JMRP.

To log in, please visit:

Please also note that since we have access to all of our IPs in SNDS, we can create, modify and delete JMRP feeds for our IPs. At this time, we do not have feeds for IPs belonging to root servers.