Cannot send an email on SMTP Port 25

Microsoft Stopped SMTP from sending emails on PORT 25.

A shocking update from Microsoft was released in March 2022 where the SMTP relay stopped working on Porta 25.

What we found:
Port 25 is stopped working with Azure VMs

What configured:
As others in the IT sector industry have configured Relay for sending an alert, notice, and bulk email to their clients, and staff we have the same configuration.

How we noticed:

In March we renewed our Azure subscription on the end date, after which all SMTP alert emails stopped sending out and piled up in Queue.

Isolated and found email not getting sent out on Port 25, we checked and our perception was right:

Now what is the reason:

For VMs that are deployed in standard Enterprise Agreement subscriptions, the outbound SMTP connections on TCP port 25 will not be blocked. However, there is no guarantee that external domains will accept the incoming emails from the VMs. If your emails are rejected or filtered by the external domains, you should contact the email service providers of the external domains to resolve the problems. These problems are not covered by Azure support.

For Enterprise Dev/Test subscriptions, port 25 is blocked by default. It is possible to have this block removed. To request to have the block removed, go to the Cannot send email (SMTP-Port 25) section of the Diagnose and Solve blade in the Azure Virtual Network resource in the Azure portal and run the diagnostic. This will exempt the qualified enterprise dev/test subscriptions automatically.

After the subscription is exempted from this block and the VMs are stopped and restarted, all VMs in that subscription are exempted going forward. The exemption applies only to the subscription requested and to VM traffic routed directly to the internet.

For reference: Troubleshoot outbound SMTP connectivity in Azure | Microsoft Docs



Based on this, that day is not so far when MICROSOFT will block Port 25 permanently. Now, what happens to those organizations that have all servers in Azure.

As Direct Send and SMTP relay both only work on Port 25. Better to stick with an on-prem or VM that has Port 25 open apart from moving or migrating to Azure VM.