Problem with email deliverability to Outlook, Yahoo, Gmail etc


Active Member
Feb 17, 2020
Tirane, Albania
cPanel Access Level
Root Administrator
Hi all,

Hope you are well.

I administrate a cpanel shared hosting server and accounts which are hosted there have problem with sending emails to Outlook, Gmail, Yahoo etc.

First case is:

It returns error below:

host []
SMTP error from remote mail server after pipelined MAIL FROM:<> SIZE=1619:
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 []

Second case is:

Email is delivered to spam folder of recipient

I would emphasise that this ip is not blacklisted. Also it is the same problem if i change this ip to secondary ip of this server as i have tried.
I have enabled dmarc dkim and spf records and they are set correctly.

What should i do then ?

Thank you in advance



Well-Known Member
Jun 9, 2020
cPanel Access Level
Root Administrator

The error message clearly shows that the IP is blocked at the provider side. You have to reach out to Hotmail to request delisting which could be a hassle sometimes :(


Jurassic Moderator
Staff member
Oct 19, 2014
cPanel Access Level
Root Administrator
@andrew.n is correct - that error message does indicate that you are blocked by Outlook. While you may not be blocked on a public list that you can check with a tool like Email Blacklist Check - IP Blacklist Check - See if your server is blacklisted or - Blacklist, Whitelist and FCrDNS check tool, all the major email providers, like Google and Outlook and Hotmail, all maintain their own internal blacklists.

Since the mail is being blocked by Outlook you will need to contact them directly to see what the problem is.

If other providers are also blocking the message or filtering your content to the spam folder, you would need to contact them directly as well to see if they can help you fix that.


Well-Known Member
Nov 20, 2014
cPanel Access Level
Root Administrator
As Outlook, Yahoo and Gmail are all different providers, then your server has done something serious.
If it's a shared server, then this could be out of your control.
Another account on the server is probably sending spam, so all accounts on the whole server have been blacklisted.

If this is the case, then I would suggest reaching out to your server provider/data centre.
If you own your own server and it's not shared with anyone, then you'll have to find which account is causing this.

here's a link to ask for delisting from MS

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