Do you turn an email into an Azure DevOps Work Item before starting work?
If a product owner sends an email to the development team with a request, that email should be turned into an Azure DevOps Work Item before any work is started or the work is prioritized on the backlog.
If the email's contents or subject do not need changing, then no response email is required. This would create another unnecessary email in the world.
However, if the subject is unclear, send a response as per the rules Do you know when you should change a subject? and Do you realize the importance of a good email Subject?
If the request from the client is too large for one Work Item, then it will need to be turned into multiple Work Items as per the rule Do you keep your PBIs smaller than 2 days' effort? In this case, you will need to let the client know this and include URLs to each Work Item.
Note: Once you've moved the email into Azure DevOps as a work item, you should delete the original email from your inbox or move it to an Outlook folder called "Moved to Azure DevOps" to avoid duplication.