MailCOPA won't set itself as the default email client on Windows Vista/Windows 7
Windows Vista and Windows 7 work a little differently to previous versions of Windows when it comes to default applications and security prevents applications configuring themselves as defaults. As a result the MailCOPA email software can't configure itself as your default client.
To configure the MailCOPA email software as the default email application you need to go to your windows Start menu and select Default Programs.
Click the Set your default programs option.
Select MailCOPA from the list of programs, the click Set this program as default followed by the Ok button.