Question : Which Email program was used?

I am copying files from an old hard drive (only a couple of years old) to a new computer.
The new computer is running Windows 7 and the old hard drive used to run Vista.
I would like to import old emails, address', etc from the old hard drive to Windows Mail on the new computer but do not know what to import because I don't know the email program that was being used on the old computer.
The old hard drive is physically attached to ther new computer via a USB port
I have searched for pst extensions but can't find any so I assume outlook wasn't being used.
Any suggestions as to how to determine what email program was being used on an old hard drive?

Answer : Which Email program was used?

In my Windows 7 machine, in .... \Local\Microsoft\ where Outlook lives, also lives Windows Live Mail and in that folder lives a folder called by a portion of my email address as well as a file called Mail.MSMessageStore and other files as well. I have no email in Windows Live Mail, so I cannot tell you what extensions, but if you find these folders on the Vista disk, you should find your email.

The Vista user could also have been using a different email system altogether, or using web mail.
... Thinkpads_User