There is a line missing from the code.
Immediately after
there should be a line
Code:
If .Tag = 0 Then GoTo lbl_Exit
which will allow you to click CommandButton2 to cancel the process.
What 'button'? For running the process, create a button on the ribbon/QAT (Quick Access Toolbar) to run the macro 'ReplaceFromUserForm'
This will open the userform and allow you to enter the data, then the message is created.
You may run into problems with Outlook security - in which case see
http://www.gmayor.com/create_and_employ_a_digital_cert.htm