How to change the Default Mail Client ?

Step 1) Go to run and type regedit and hit enter

Step 2) Now go to HKEY_CLASSES_ROOT\mailto\shell\open\command.

Step 3) Under command, enter the full path to the email client then %1

For example :
c:\internet\Netscape\program\netscape.exe %1
c:\program files\internet explorer\iexplore.exe %1