Hello CuriousWebbie,
If you cannot locate the 10.6 Mail app, you may have to reinstall it using the original installation media. I have located an article that explains the process:
Mac OS X 10.6: Reinstalling applications that came with your computer
If you delete an application that came with your computer, you can reinstall it if you need to.
If you want to reinstall an application using the optical drive from another computer on your network, use DVD or CD Sharing. For more information on DVD or CD Sharing, see:
Using another computer’s DVD or CD drive
To reinstall an iLife application (iPhoto, iMovie, iWeb, iDVD, or GarageBand):
Insert the Applications installation disc into your computer’s optical drive (or an optical drive connected to your computer) and double-click the Install Bundled Software icon.
Note:If your computer came with an iLife installation disc or you purchased a newer version of iLife, insert that disc instead, and then follow the onscreen instructions.
Follow the onscreen instructions. In the Installation Type pane, click Customize.
Click the disclosure triangle next to Bundled Applications, select the checkbox next to the application you want to install, and then click Install.
To reinstall a Mac OS X application (Address Book, iCal, iChat, iTunes, Mail, or Safari):
Insert the Mac OS X installation disc into your computer’s optical drive (or an optical drive connected to your computer), double-click the Optional Installs folder, and then double-click the Optional Installs package (looks like an open box).
Follow the onscreen instructions. Select the disk where you want to install the application and click Continue.
Click the disclosure triangle next to Applications, select the checkbox for the application you want to install, click Continue, and then click Install.
After you reinstall a Mac OS X application, open Software Update (choose Apple menu > Software Update) to update the application.
If you can’t find the application you want to install:
Check to see if your computer came with another set of discs.
Choose Apple menu > Mac OS X Software and search for the application.
Thank you for contributing to Apple Support Communities.
Best,
BobbyD