When using the Azure Communication Service to send emails you might want to have different sender subdomains for different stages, e.g. @example.com for production and @dev.example.com & @test.example.com for Dev and QA. Unfortunately the docs are quite unclear on how to set this up, especially when it comes to the DKIM configuration.
While the domain verification and SPF setup is quite straight forward, for DKIM Azure expects selector1-azurecomm-prod-net._domainkey as the CNAME record name. Or at least so it says.
Solution
For subdomains though it acutally needs to be selector1-azurecomm-prod-net._domainkey.test
So for both DKIM and DKIM2 append the .subdomain to your CNAME record name. Here’s the full DNS setup (in my case on Namecheap):
And here’s what it should look like in Azure eventually:
