Hotmail, Outlook, Yahoo and etc cant send mail

Operating System & Version
CentOS 7
cPanel & WHM Version


May 28, 2020
cPanel Access Level
Root Administrator
Hello everybody!
I have a problem related to Hotmail and other domains specified in the topic name.

When I send an email I get an error:

host []

    SMTP error from remote mail server after pipelined MAIL FROM: My Domain SIZE=1637:

    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 (S3140). You can also refer your provider to []

Checked your domain via:

and I do not have my domain in the spam database of Microsoft and other databases.

I think this may be a problem in txt and other DNS records..

I will explain in detail how my mail works, and I hope you will help me :)

In General, I have 2 domains and 2 servers.
The 1st server has a domain (
The 2nd server already has two domains ( and

Mail accounts and so on are installed only on the 2nd server.
The 1st server is only used for the site and scripts.

All DNS records are placed on the first domain.
The second domain contains entries only for
SPF, DKIM, and DMARC are installed correctly. But the emails are still not being sent. What could be wrong?


Well-Known Member
Jan 13, 2020
cPanel Access Level
Root Administrator
Sorry but I just have to :rolleyes: is the worst of the worst of the worst you can find on the internet. I've had trouble with them, and still have. Out of my recommendations to my customers and in general, they have lost over 500 customers already, and I will keep doing that until they fix their service. I see red every time I hear or see about them. What can you expect from MS service...

Sorry about this, but just had to.

What you can try is this:

Hope it helps!

- Wallu


Well-Known Member
Nov 9, 2001
cPanel Access Level
DataCenter Provider
The answer is right in the bounce message:

Unfortunately, messages from [] weren't sent.

It's not your domain, it's the IP (or possibly the subnet you are in). You can certainly try to contact Microsoft support for outlook, hotmail etc. but we find that to be basically useless.
  • Like
Reactions: cPanelLauren


Well-Known Member
May 22, 2020
cPanel Access Level
Root Administrator
Add a free monitor on your IP address via and if you're added to a blacklist, in all likelihood, you'll be added to the blacklist for Outlook, hotmail and so on.

Be sure to limit the amount of email the server can send so if a website gets hacked and is used to relay spam, the damage to your IP reputation is minimal.