Gmail Labs adds a new feature to save time when composing messages—it can now suggest contacts based on the groups you email most often.
Enabling the feature works the same as all the Gmail Labs options—just head to the Labs tab under Settings and turn on the option. Once you’ve enabled it, you’ll see suggestions once you’ve added at least two recipients to an email message. It’s a simple but potentially great time-saving feature—just one of many Labs features you should enable.
New in Labs: Suggest more recipients [Official Gmail Blog]