Webmail Setting for Address Auto-complete

From HostBaby Wiki

Are you looking to have your Webmail page automagically complete the email address you're writing to? Well, here's the place to do it!

If you go into the Options section of your webmail setup and click on display preferences, under Composition Options you will find the box for this feature right there. Its labeled Autocomplete addresses from Address Book, and below you'll find a picture of what it looks like:

This should be all you need!