Traffic blocked on port 25

Question

Hello!

I have a quick question regarding a query I received. I wanted to confirm whether there is any way to open port 25 for a CSP subscription.

According to the documentation, this is only supported for EA and MCA-E subscriptions, but I wanted to check if there’s any possible exception or process that would allow this for a CSP subscription.

Answer 1

Hello LeRoy, Kevin

You are dealing with an issue regarding the blockage of port 25 for a CSP subscription in Azure. Unfortunately, as you've noted from the documentation, Azure does block outbound SMTP connections on TCP port 25 for most subscription types, including CSP, to enhance security and comply with industry standards.

This restriction is in place to prevent abuse (e.g., spam) and maintain IP reputation across Azure's shared infrastructure.

Outbound port 25 is only allowed for:

• Enterprise Agreement (EA) subscriptions
• Microsoft Customer Agreement for Enterprise (MCA-E) subscriptions

Here’s a summary of the important points:

1. Port 25 Blocking: Azure blocks outbound SMTP traffic on port 25 for subscriptions that are not part of the Enterprise Agreement (EA) or Microsoft Customer Agreement for Enterprise (MCA-E). So, for CSP subscriptions, this limitation indeed applies.
2. Alternatives:
   • It's highly recommended to use an authenticated SMTP relay service instead. This usually involves connecting via TCP port 587, which is open and suitable for sending emails. Microsoft provides services like Azure Communication Services, which can be a good alternative for sending emails from Azure.
   • Azure App Service and Azure Functions can also send outbound traffic on port 25 under certain conditions (like virtual network integration), but this isn't applicable to all services.
3. Requesting Changes: For enterprise-level subscriptions when it’s critical to send emails directly through port 25, there are processes to request changes, but this isn't available for CSP subscriptions.

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