Yes and no.
The proper way of doing it is by opening the Exchange System Manager (Start, All Programs, Microsoft Exchange, System Manager). Then go to the Mailstore in question (Administrative Groups, First Administrative Group, Servers, [Server Name], First Storage Group). Then right click on the Mailbox store and click "Dismount Store". To Mount it, right click on the mailstore again and click Mount Store.
Starting and stopping the service does dismount all mail stores as well, and generally does so safely. But I'd still recommend doing it by following the directions above.
