SQL Server Agent/Properties/Alert System/Mail Session/Test is disabled In order to enable operator notifications I navigated to SQL Server Agent/Properties/Alert System/Mail Session, checked "Enable mail Profile", selected Mail System and Mail Profile. At this time Test button next to the Mail Profile was disabled, so I clicked OK and decided to return to this configuration dialog later.

This worked and notification are being sent but when I returned to this configuration dialog later the Test button is still disabled.

Can anyone explain that?
Test button referred in the question is only available for older version of SQL Servers that supported SQL Mail. Below picture is from a SQL2008 SP4 instance where you can use the test button.



From books online:


  SQL Mail is not installed by default in SQL Server. For more
  information, see Understanding Surface Area Configuration. SQL Mail is
  not supported on 64-bit versions of SQL Server. SQL Mail stored
  procedures cannot be installed on 64-bit versions.


For Database mail you can use this feature for testing.

Using SSMS, Instnace-->Management-->Database Mail-->Right click-->Sent test Email.