For Thunderbird you could use the Shell function.
Here is an example I found that adds text to the body and attaches a file.
Shell ("C:\Program Files (x86)\Mozilla Thunderbird\Thunderbird.exe -compose to='mymailname@gmail.com',subject='Test message from thunderbird',preselectid='id1',body='Example message from myText.txt',attachment='file:///c:\onwin.png'")
This website provides the command line arguments for Thunderbird:
http://kb.mozillazine.org/Command_line_arguments_(Thunderbird)[
^]
Good luck