"I'm getting an error when sending emails to Microsoft emails via webmail."

Hello friends,

I have an Armalinux cyberpanel server.

I’ve been using it for 7 to 8 months without any problems, but let me tell you about the issue I experienced three days ago. I kindly request information from experts.

For example, the admin domain address of the server is:

There are 50 users/customers and 50 sites under it.

Now, for instance,


My customer’s site has an [email protected] webmail address. When sending emails to addresses with hotmail extension, I receive an error mail. The error mail is as follows:

This is the mail system at host b.com.

I’m sorry to have to inform you that your message could not be delivered to one or more recipients. It’s attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can delete your own text from the attached returned message.

The mail system:

[email protected]: host hotmail-com.olc.protection.outlook.com[] said: 550 5.7.1 Unfortunately, messages from [] 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 Troubleshooting. [DB1PEPF000509E9.eurprd03.prod.outlook.com 2024-04-09T11:48:03.393Z 08DC53D5F8ECC613] (in reply to MAIL FROM command)

Sender: Poyraz

To: [email protected]

Sent: Tue Apr 09 14:48:00 GMT+03:00 2024

Subject: Information request

Hello Mr. Poyraz,

The webmail address of a.com, my customer, is sending mail to hotmail extension, but the text above in the error mail says:

This is the mail system at host b.com.

It mentions a different customer’s domain on the server.

When I checked the host address of the server via SSH, I saw that it was the normal admin domain.

All sites’ zone DNS settings are correct, and mail services are working.

The server already has a cloud IP address, which is a shared IP address.

Other servers using this IP address might have been blocked by Microsoft.

I applied to Microsoft to lift the ban on the IP address, and the process is ongoing.

My question is:

Why does the error mail show the domain address of another customer instead of the admin domain in that field? It should have shown the admin domain.

b.com must be configured as hostname in postfix. This also happens from here: Onboarding and Initial CyberPanel Configurations – Knowledge Base