Hello @Jeff White , Thanks for asking this on the Microsoft Q&A platform. I understand you’re trying to modify the email sent from Test Plans when assigning testers. I reproduced the scenario on my side as well, and the behavior matches what you’re seeing.
At present, Azure DevOps does not provide a way to edit or customize the built-in “Send email to testers” template. The only editable portion is the optional note that appears in the email. If you need a custom layout or additional information in the email, the recommended approach is to send a separate email outside Azure DevOps or automate this through a workflow such as Power Automate so you can define your own template and formatting.
If this capability is important for your workflow, I’d suggest submitting it as a feature request so the engineering team can consider it for future updates:
https://developercommunity.visualstudio.com/AzureDevOps/suggest
I hope this clarifies your query. Please do let us know if you have any further questions on this. Feel free to upvote the comment if it helps. Thank you!