I am the CTO of a ISP. The ISP I work for uses it's own IP Addresses and I have no problem sending emails to and receiving emails from Hotmail and Outlook.
The problem is that I am migrating some e-mail servers to the cloud and every single one of them is being blocked by Hotmail/Outlook.
I've even built a new server from scratch on Azure, using Microsoft's own infrastructure and IPs and the e-mails are being blocked.
My last (current) try was using Oracle Cloud. I have a new e-mail server there with everything correctly configured, including reverse DNS, SPF, DKIM, DMARC, TLS, etc. The IP I am using has never been used before. And yet it is being blocked by Hotmail/Outlook. Every other e-mail service including Office365 accepts my e-mails without any problems. Only Microsoft's free e-mail services are the problem.
This is the message I always get:
Remote Server returned: '550 5.7.1 Unfortunately, messages from [18.104.22.168] 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
I've tried requesting the block removal but I always receive the same default answer: Not qualified for mitigation. Our investigation has determined that the above IP(s) do not qualify for mitigation.
I even contacted Azure's specialized support (when I was testing the e-mail server on Azure) and they told me to use the default Hotmail Blacklist Removal Form - https://support.microsoft.com/en-us/supportrequestform/8ad563e3-288e-2a61-8122-3ba03d6b8d75 - but I always get the same default answer.
So... what's going on? Why is Hotmail/Outlook blocking every new IP address? I can't migrate or create any new e-mail server because of this. Unfortuntely a lot of offices/companies use Hotmail. My costumers won't accept a service where they can't send/receive to and from Hotmail/Outlook.
Does anyone have the same problem? Can anyone from Microsoft help me?
** Moved from: Outlook.com / Email / Sending, receiving, and reading email **