Send emails via SMTP relay with Azure Communication Services

We’ve come across multiple cases where customers want to send emails from applications migrated to Azure through some kind of SMTP service. Though we’ve seen customers opting for O365 for SMTP relay, this can create issues due to throttling limitations in Office Service. Also, managing mailbox and license assignment on Office 365 console is a different story; customers would want to have seamless SMTP relay service experience from single console on Azure.

In scenarios where you don’t want to modify code and just change the pointing of your SMTP server to Azure, you can now use SMTP relay built into Azure Communication Services' Email.

Azure Communication Services supports different types of notifications, and this blog post offers simple step by step instructions for how you can quickly test and then migrate from other services you’re using to native to Azure for better operational experience and support.

Create Azure Communication Services Resource

First step you’ll need to do is to create a Communication Services resource from the Azure portal. This is a parent service which has multiple notification services inside it (Chat, SMS, Email, etc). Email is one of them.

Create an Email resource

Add a custom domain

Azure Communication Services Email will provide a default domain that looks like this “GUID.azurecomm.net” and allows for a limited volume of email, so if you need more volume limits, we recommend creating a custom domain. Once you add a custom domain, the UI provides you with a TXT file which you’ll need to create in your Name server. This would take 15 minutes to verify the domain

Once the domain is verified, create SPF and DKIM records so that your email doesn’t land in junk and ownership is maintained.

Once all the records are created the screen would look like this, please ignore the Azure managed domain. You can only have custom domain in the account and doesn’t have to add Azure domain explicitly.

Attach custom domain 

Once the custom email domain is validated, we’ll need to attach the Email service to the Azure Communication Services resource. 

Create and assign custom RBAC Role for Authentication

We’ll be using 587 port to send email which is authenticated SMTP. For authentication we have Entra ID authentication. Create a service principal by going to Entra ID – App registration page. Register the app and create a client secret. Note down Client ID, Tenant ID and Secret value. This will be used in next stage for authentication. We’ll need to create a custom RBAC role which has permission to send email. We’ll clone reader role.

And we’ll be adding two actions which is present in Azure Communication service resource provider.

Once the Role is created we’ll need to assign this to service principal

Test SMTP Relay via Powershell

That’s all, now you’ll need to find out the sender email. Which is default DoNotReply@domain.com

You’ll need credentials to authenticate to the service.

• Username is < Azure Communication Services Resource name>. < Entra Application ID>. < Entra Tenant ID>
• Password is the client secret which you’ve generated.
• Port that we’ll need to use is 587
• SMTP server address is smtp.azurecomm.net

Now you can use any third party application to send email via the above parameters. To showcase we can use PowerShell with the same parameters to send emails.

Conclusion: I trust this guide helps you in configuring SMTP relay and send emails from your custom application without any change to the application/code.

Happy Learning!