SQL Server 2016 Database Mail Is Not Working

If you are working on SQL Server 2016 and your machine is having .NET Framework higher than 3.5 then you will not be able to send using DB email.

As Per Microsoft Support, there's a bug in SQL server 2016 Setup that causes the database mail not to work without .net 3.5. So they provided a workaround for this bug  by creating a DatabaseMail.exe.config file. The steps to create this file are as below

Create the DatabaseMail.exe.config and drop it next to the DatabaseMail.exe under the Binn folder. You can use notepad.exe or any other editor to edit it. Just make sure you save it by using UTF-8 encoding (in notepad.exe, select Save As... and in the Encoding combo box, select UTF-8): 

         <?xml version="1.0" encoding="utf-8" ?>

         <configuration>

         <startup useLegacyV2RuntimeActivationPolicy="true"> 

         <supportedRuntime version="v4.0"/>     

         <supportedRuntime version="v2.0.50727"/>

         </startup>

         </configuration>

Note:

Sometimes I have observed that the config file get disappear automatically after reboot. So, to fix that you can create a SQL agent job which will create/copy this file (DatabaseMail.exe.config ) in Binn folder and schedule to run it after every service reboot. This way you can overcome with this issue.