Under File > Export you can select to export all your data as .olm file. This file can be used as backup or to move your data into a new Identity. Do you get “Done” at the end or do you get “one or more items failed to export”? If you do not get “Done”, all your data was not exported.
If you are using the .olm file to create a new identity, I suggest you delete your Exchange and IMAP accounts after putting Outlook into Work Offline before exporting.. (Be sure to create a copy first of your Identity before deleting accounts.) This deletes the cache files in Outlook but not on the server. Now you only have to deal with “On My Computer” messages. You can download your Exchange and IMAP emails in the new Identity.
After exporting you should get Done!
If you have set to partially download messages, you will get a message saying some items might still on the server. This is OK, but if you get a message that one or more items failed to export not all data was exported. It’s possible you have corruption but your first step is to look for folders with over 2GB in data. Usually this is the Inbox and Sent folders. If you have archived data, be sure to check this folder too.
I often see users have mail going back several years especially in the Inbox and Sent folders. I find that if you create subfolders e.g. Inbox 2011, Inbox 2010, Sent 2011, Sent 2010 etc. this usually gets the folders under the 2GB limit. Only Exchange accounts will give you a folder size. From experience I find between 6,000-10,000 messages will fall under the 2GB limit. If you drag a folder to the Desktop and it’s 2GB, most likely you still need to further prune that folder.
Folders by year will never change. By dragging these older folders to the Desktop as .mbox file, you will have archived that data. You will always be able to add this data back if your Identity is lost or damaged.
After pruning your folders, now try File > Export all items as .olm file.
If you get Done, you can use the file to create a new Identity.
If it fails, there is corruption in your data. Previously, in Entourage we had a free script to export folders as .mbox file that would help identify folders with corruption. This script no longer works in Outlook. You can download and try the EmailChemy demo to see if it will export all your data as .mbox file before purchasing. It’s $29.95 to purchase.
Outlook requires that you import .mbox files one at a time. If you have a lot of folders this can be very time consuming. EmailChemy can convert a folder of .mbox files into a .olm file for easy import into your new Identity.
If you need to move to Apple Mail from Outlook, this is your best option if you have a lot of folders that are not on the server.
For help moving the imported data into the local folders see How to move your data to a new Identity step 10.