You should be able to re-install it using the Vista's Add/Remove Windows Components
To Add/Remove components in Vista, do the following:
- Open
Control Panel
- In the
left hand pane choose
Classic View
- Double click
Programs and Features
- Look in the
left hand pane and click on
Turn Windows Features on or off
- Once the box is
updated you will be able to Add/Remove Windows Components
Add Windows Mail as required
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If that doesnt fix it you may find a solution
HERE