If you use Entourage 2004 or 2008, I believe that it’s critically important that you backup your Entourage database daily or even more often.

Entourage stores all of your email messages, calendar events and address book contacts in the database file. As this database file gets larger it becomes more and more prone to getting damaged. Some damage can be repaired, but it’s not uncommon for some databases to be damaged beyond repair. At this point there are typically only two ways to deal with the situation. The first option is to manually rebuild your database which is very time consuming and almost certainly ensures that some email messages or other data will be lost. This process requires you to manually export your address book, calendar events and then export each mail folder one by one into individual mailboxes (mbox). The second option is to restore your Entourage database from a recent backup. Your backup copy of  your Entourage database will still be large and in need of some housekeeping, but hopefully its not damaged so you can do this clean-up and avoid future problems. The more frequent your backups the better since we want to work with a recent database.

I should also emphasize that it’s important to deal with a damaged Entourage database at the earliest sign of problems. In some cases Entourage will display a message indicating that your database is damaged. In other situations you’ll notice problems. Entourage might display multiple copies of the same email message in your inbox. Or, it might display the header information for one email message while displaying the body of a different email message.

You can manually start Entourage’s built-in Database Utility by holding down the option key while opening Entourage. It’s recommended that you choose the “Verify” option to check the health of your Entourage database.

Be aware that if you use Entourage 2004 the “rebuild database” option in the Database Utility removes all category information that you’ve assigned to contacts and email messages. I believe it also deletes all of your Notes. These problems were apparently fixed in Entourage 2008, though I haven’t verified that personally.

Entourage stores its database in this location:

/Users/<your username>/Documents/Microsoft User Data/Office Identities 2004/Main Identity

Note: If you’re using Entourage 2008 then the folder name changes to Office Identities 2008.

To backup the database I recommend copying the entire Main Identity folder. Look inside this folder to make sure that the database file inside was modified today. This way you can be more certain that this is your current database. Entourage lets users create multiple Identities so you could have more then one identity folder. If you’ve used the Database Utility to repair your database then you may find more then one database inside the identity folder.