Usually after 90 days or you reach 1,000 emails in your inbox, the oldest messages will be moved to a folder in webmail called "old-messages". You can access those emails via webmail at anytime, but for convenience sake, you can add your old-messages folder to outlook. See below for instructions:

1. In Outlook, right click Inbox in the left hand pane 2. Choose IMAP Folders... 3. Click Query 4. Scroll through the folders listed and select old-messages 5. Click Subscribe, Apply, and then OK

Now give Outlook some time to synchronize that folder and when it is finished, all of your archived email will be available within Outlook.