When trying to send email to clients who use Hotmail/Outlook/etc type email addresses, I get the following error:

SMTP error from remote mail server after RCPT TO:[email protected]: 550 5.4.1 Recipient address rejected: Access denied. AS(201806281) [HE1EUR01FT049.eop-EUR01.prod.protection.outlook.com]


SMTP error from remote mail server after pipelined MAIL FROM:[email protected] SIZE=2699: 550 5.7.1 Unfortunately, messages from [IP ADDRESS] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150).

My email is hosted on a cPanel shared server, most of the domains are under my control. When checking the server IP address, I can find no blacklisting.

I have contacted Microsoft who comes back with an unhelpful canned message basically stating that they can not help.

So what it seems is that an IP in the same network as ours, is blacklisted, and for this reason, our mail is being blocked.

(DKIM/SPF are all installed).

Can anyone advise how to diagnose and find the culprit causing our server IP address to be blocked?

3 Answers 3


It seems this is currently the address for the delist interface: https://olcsupport.office.com/


If the IP ranges are blacklisted then as a customer you cannot WHITELIST on your own

It requires your (Hosting) network administrators to submit the request to (outlook/hotmail) through there organization mail id, will only help in removing the blacklist and change its reputation

Reaching out the hosting provider along with bounce/failure message will help you.

  • I took the IP range and went through each IP one at a time and checked against Spam databases. As fortune would have it, the last IP in the range was listed. This was the broadcast IP. Had it removed - I guess now I wait to see how long it will take for Outlook to update its Blacklist.
    – HappyCoder
    Jul 7, 2020 at 19:57

Maybe MXToolBox could help you check if your server IP address/domain was added in the blacklist, and find the possibile reasons why your server IP address was blocked.(Enter your server IP address/domain to diagnose.)enter image description here

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