Outlook/Hotmail is no longer blocking my mail server

2023-12-23 ⏳2.0 min(0.8k words)

Comments on Hacker News:


After some struggle, I managed to de-list the address of my mail server from Microsoft’s blocklist. Here is some experiences may help you.

I am running my mail server on one Oracle Cloud Computer, which has no cost. You can read my another blog post1 to dig the setting up details. After all work has been done, I can deploy mail to all major Mail Service Providers like Gmail, Yahoo Mail, QQ Mail, and so on. My employer uses the enterprise edition service of Office365. And I send testing mail to it, no problem has been found. Since I do not own a personal account of Outlook or Hotmail, I do not test mail to the domain of outlook.com/hotmail.com, assuming there is no problem.

One day some reader of my blog leave a message to me and He uses a mail address with the domain of live.com, which is part of Outlook/Hotmail. When I try to reply his message in my mail client, it received the following error message:

Delivery to xxx@outlook.com failed with error:
outlook-com.olc.protection.outlook.com. said:

Unfortunately, messages from [xx.xx.xx.xx] weren't sent.
Please contact your Internet service provider since part of their network
is on our block list (S3150). You can also refer your provider to

[BN7NAM10FT025.eop-nam10.prod.protection.outlook.com 2023-12-15T15:17:55.319Z 08DBF7ED000951E3]

Diagnostic-Code: smtp; 550 5.0.0 outlook-com.olc.protection.outlook.com.

I opened the link it offered. In the section Sender services, tools, and issue submission, they offers a link to create support list. You need an account of Microsoft to submit request, and I registered one with my own email address and some fake contact information, because I do not want to lave too many of my personal data to Microsoft. It take several days that Microsoft replied my request with Email. However, the reply is very frustrating, because it said that they do not block mail from my IP address.

Hi ,
Thanks for your patience while we investigated your request.
Below your IP address(es) and their status(es) are listed.


Nothing was detected to prevent your mail from reaching Outlook.com customers. Please follow the instructions below.

Still need help?

If you have additional questions or still experiencing deliverability issues or want further investigation, please reply to this email with the following information and an advocate will respond to you by via email.
Relevant IP addresses(es)
Detailed description of the problem you are having
specific error message(s)

According some article from the Internet, I replied the mail immediately with the following content:


Thanks for replying. 

You say my IP address XX.XX.XX.XX was not prevent from reaching outlook.com.
However, I still can not send email from XX.XX.XX.XX to outlook.com customers.

Here is the error message:


XX.XX.XX.XX is my own personal email server, with controlled user creation access.

This is a newly acquired IP address.

    This server is used solely for the purpose of mailserver, with ssh
    access only granted to an administrator.

    The server is also configured with all the necessary records to ensure
    only authenticated users connected to our secured smtp can send mails
    from our domains.

Microsoft never reply my mail. Three days later, I resend another mail trying to persuade them to unblock my server. In the mail, I explained this is an indie mail server and for personal usage only. I also try to let them understand that I am not an spam sender by offering relative content of my blog. Maybe the fake contact information of my Microsoft Account make them worry that I am not a good guy. Here is the full content.

Sorry for replying again.

I still can't delivery email to outlook/hotmail now.

This server is my personal mail server for my own usage.
I have setup only one month ago.

I am also writing on my blog, and the readers may contact me by this mail server.

My blog URL is https://taoshu.in/ and the setting process was recorded at


Some readers contacted me by hotmail/outlook, and I can't reply to them.
That's when I discovered I hotmail/outlook has blocked my server.

The IP XX.XX.XX.XX I am using is from Oracle Cloud, and it is not in any public blacklist according to mxtoolbox


I have not, and will not to try to delivery bulk mail or spam mail to outlook/hotmail or any mail service provider.

Please consider to unblock my IP.


Still get no response. So I tried to contract to Oracle Cloud and wished they could offically communicate with Microsoft and make their IP address range unblocked. Unfortunately, they did not offer any help.

Thank you for your response. Unfortunately, we do not have any power or say
when it comes to blacklists from third-parties. You would need to continue
to work with Microsoft in order to resolve this issue.

I have no choice but wait the response from Microsoft.

Five days passed, there still no reply. But today I login the server and try to connect the MX server for Outlook/Hotmail by telnet. After I sent the command of mail from, the other side responded 250 2.1.0 Sender OK. I known Microsoft has finally unblocked my mail server. Cheering up🍻

If you also encounter this kind of problem, do not be afraid. You are not alone. So many people have replied this thread2, complaining Outlook/Hotmail block their mail server unreasonably. It is a problem for self-mail-hosting, however, it can be addressed. So don’t be intimidated by this difficulties.

According to my experiences, although Microsoft may block some IP range, it does not intend to do so. This blocking policy is only one stress measure for the increasingly rampant Spam problem. They are just not very friendly, but never hostile to self-mail-hosting. If you encounter this kind of issue, using a normal Microsoft Account with real contact information and submit request with detailed information may address you problem.

So many words have been said that you should never run your own mail server. I beg to differ on this point. Because Email is the only successful federate system that is always defending the foundation of the freedom of the Internet. Every one should have the freedom to run their own mail server and communicate with each other freely. So we should defend the right for self-mail-hosting.

  1. ./selfhost-email.html↩︎

  2. https://answers.microsoft.com/en-us/outlook_com/forum/all/hotmailoutlook-block-list-s3140-blocks-all-new/699f3a56-406e-4804-97e2-cbe23b9bb01c↩︎