Backup Windows Mail Contacts
Besides backing up your email messages, you need to backup your email contacts or as most call it, the address book.
It would seem like it should be included with the message backup, but sorry to say it is a separate backup.
Vista uses a 'Contacts' file and hides it in appdata which is a shortened name for the old applicationdata in Windows XP. (This was not easy to find unless you enabled viewing hidden files and folders.)You don't have to worry about that location as you can just export the contacts to a file and put that file in the newly made folder named 'Mail Contacts' in your documents folder.
Open Windows Mail and click on File on the main menu and select 'Export' then 'Contacts'.
Now you will be asked to name and browse to the location to save the file. (I named my file 'my contacts')
Windows Mail will ask you what format to choose and you should select the second one 'CSV (Comma Separated Values). This format is used by most email address book imports and can be used by Thunderbird, Gmail and others.
Once you have selected the file format you will be asked to choose what fields to export. You can just use the default or you can select or de-select as you will.
Here are some screenshots that follow the above process.