If you want to make sure you have exactly the same e-mail messages—including all your saved and sent mail-on two or more Macs, there’s an easy way and a hard way to do so.
Server-Based Accounts The easy way, which works with almost any e-mail client, is to not sync your e-mail at all, and to instead use a server-based account (.Mac/MobileMe, IMAP, or Exchange). With these accounts, all your incoming, saved, and sent mail is stored on a mail server. You can configure your e-mail program to keep local copies of all your messages, too, so that you can read and search them even when you’re offline.
Your existing e-mail provider may already offer IMAP access to your mail (Macworld.com has
more advice on using IMAP, including switching from POP). Another option, available to everyone, is to get a free, IMAP-capable Google Gmail account.
Local E-mail Messages If you’re stuck with a provider (say, your employer) that provides only POP-based access to your e-mail, or if despite having an IMAP account you’ve stored some of your messages locally on your Mac, you’ll have to turn to file-based synchronization.
You can, of course, simply copy all the files that pertain to your e-mail from one Mac to another. However, both Mail and Entourage throw wrenches into the works. Mail stores all your messages as individual files, but it also relies on a database to store an index of your messages for faster display and searching. You can synchronize two folders with different sets of messages easily enough, but if you try to synchronize the database files, one will entirely overwrite the other, so Mail’s message lists will be incorrect. Entourage, meanwhile, stores all your e-mail data in one huge database file. So once again, while you can synchronize that file between Macs, you can’t synchronize individual parts of it—if you’ve received messages on both computers since your last sync, there’s no way to merge the two databases. All is not lost, though; you just have to be very careful in how you proceed.
To sync Mail messages, first make sure Mail isn’t running on either computer. Using your favorite sync utility, synchronize the entire Mail folder (your user folder/Library/Mail) bidirectionally between your two Macs. (This synchronizes everything, including On My Mac mailboxes, rules, and junk-mail statistics.) Then—only after the first time you do this—navigate to that Mail folder in the Finder on each Mac and drag the Envelope Index file to the Trash. Launch Mail and allow it to reimport your messages (which means it’s really rebuilding your message database). Quit Mail on one of your Macs. From now on, be sure you run only one copy of Mail at a time. Before switching to the copy running on your other Mac, use your synchronization utility to resync the Mail folders.
With Entourage, your only option is to entirely overwrite one computer’s copy of the database with the other’s copy. If the two have different sets of messages before you start, you’ll lose data. Therefore, your best bet by far is to switch to IMAP or another server-based account, so that syncing becomes automatic. However, if you’re sure that one copy of Entourage is a superset of the other (so you won’t lose any messages by overwriting the other one), you can sync one Mac’s copy of the Entourage database to the other Mac. To do this, make sure Entourage isn’t running on either computer. Use the sync utility of your choice to synchronize your Entourage database between your two computers (by default, it’s located at /your user name/Documents/Microsoft User Data/Office 2008 Identities/Main Identity/Database). Thereafter, make sure you run only one copy of Entourage or the other at once, and that you immediately sync your databases after each use.