Request to unblock outbound SMTP port 25 for email delivery

Hi Seo Jin-sook

Welcome to Microsoft Q&A .Thanks for posting the below query below

I see you need to unblock outbound SMTP port 25 for email delivery from your Azure VM. Here’s what you can do based on your subscription type:

Identify Your Subscription Type:

• If you're on an Enterprise Agreement or Microsoft Customer Agreement (MCA-E), port 25 should not be blocked for your outbound SMTP connections, but there's no guarantee that external domains will accept your emails.
  • If you're on an Enterprise Dev/Test subscription, port 25 is blocked by default. However, you can request to have this block removed by running a diagnostic in the Azure portal under the "Cannot send email (SMTP-Port 25)" section.
    • If you’re using another type of subscription (like Pay-As-You-Go), port 25 is blocked, and you will need to use an authenticated SMTP relay service instead.
    To Request Removal of the Block (for Dev/Test subscriptions):

    - Go to your Azure portal and navigate to the **Diagnose and Solve** section for the Azure Virtual Network resource.
    
       - Run the diagnostic for **Cannot send email (SMTP-Port 25)**.
    
          - After the exemption is applied, you need to stop, deallocate, and restart your VMs for the new policies to take effect.
    
          **Use an Authenticated SMTP Relay**:
    
             - Even if you can unblock port 25, it's recommended to use an authenticated SMTP relay service (like Azure Communication Services or SendGrid) to ensure better email deliverability. These services typically connect via TCP port 587, which is not blocked.
    
             **Verify Connectivity**:
    
                - After making changes, you can verify outbound connectivity by using PowerShell commands like `Test-NetConnection` for Windows or `nc` for Linux to test your connection to a mail server on port 25.
    

Here are some handy links for further reading:

• Troubleshoot outbound SMTP connectivity problems in Azure
• Azure network security groups overview
• Recommended method of sending email

Hope this helps! If you have any more questions or need further assistance, feel free to ask!

Regards

Jose