Different kind of archives
Entourage Email Archive X is an utility for archiving emails and attachments you have received or sent using Microsoft Entourage in Mac OS X.
EEAX can archive your emails in seven different ways with further sub-options.
Emails backup and restore
One of the features of EEAX is to archive emails as native Entourage file format.
The files with .eml extensions give you the possibility to restore one email or group of emails simply drop them back to Entourage at any time.
This feature will let you restore the archived email even with future versions of Office.