Mine seem to be in Documents/Microsoft User Data/Entourage Temp.
That's where attachments you send and receive are stored so that you can see
them. That folder should be emptied each time you quit Entourage.
That's just a place you can choose to save attachments.
No, a Typical Rebuild does not delete attachments. You could select all
messages in a folder (Edit -> Select All) and then do Message -> Remove All
Attachments. You'd want to save attachments before doing so.
One way to keep your database slim and save attachments from incoming mail
automatically is to use Friendlier Claris It.
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http://homepage.mac.com/robbuckley/>
You could also create a rule to remove attachments from sent mail, like the
one here:
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http://www.entourage.mvps.org/rules/rules.html#anchor-rule1>
By the way, it's been recommended that regular rebuilds be avoided unless your
database has increased to an unmanageable size and needs to be reduced or if
you begin to experience symptoms of database corruption.