After you send many email messages by using SQL Server 2016 Database Mail, your CPU usage is higher than expected.
This issue occurs because Database Mail creates an orphan System.Timers.Timer object in every loop iteration of the queue processor.
Each new cumulative update for SQL Server contains all the hotfixes and all the security fixes that were included with the previous cumulative update. Check out the latest cumulative updates for SQL Server:
Latest cumulative update for SQL Server 2016
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Learn about the terminologythat Microsoft uses to describe software updates.