Archive Your Data
An Archive contains copies of your files as they appeared at multiple points in time. You can archive your Entourage data in a separate Identity, an MBOX file or as an Entourage archive (.rge).
If you want quick access to your archived mail, I suggest creating a new Identity that will allow you to quickly "Switch Identities" to view old mail. Some users do this yearly.
If you simply wish to have snapshots of your data to use in case of database failure, archive your Identity as an Entourage archive (.rge) or as an MBOX file. Organize your archives using FolderOrgX.
Another option is to use a third party application to store your emails. One free option is to use eMessage Archiver. It uses a free runtime version of FileMaker.
Options to Create an Archive Identity
1) Duplicate your current Identity and rename it. Now, you have a duplicate Identity folder structure with your old mail that you can quickly switch to for easy searching. Remove Old messages from current Identity using a Custom View. Leave at least 60 days of old mail. You will have some duplicates but this is preferable to switching Identities constantly to find recent mail.
2) Create a new Identity and import mail from an Entourage archive (.rge) or drag an MBOX file into the folder window. You can also use a custom view to create an MBOX file.
Custom View to remove old mail (Learn about Custom Views)
Step 1. This view will get all mail that is older than 60 days. Set date according to YOUR needs.
Step 2. Select the new mail view 
Skip steps 3 and 4 if you duplicated your Identity and do not wish to create an additional MBOX file as backup.
Step 3. Drag it to the desktop 
Step 4. An MBOX file is created. 
Step 5. Select all of the messages in custom view and delete.
See movie on using MBOX files.
(.rge file extension)
Starting with Entourage 2004, you can export items such as mail messages, tasks, contacts, notes, and calendar events to an Entourage archive (.rge extension). This enables you to store information in another location and remove it from Entourage. You can also use this process to make a back up of your Entourage information (without removing the information from Entourage). See movie on using Entourage Archive files.
