Yes, you can import historical emails from Outlook to FYI.
There are two options to achieve this. Please refer to the below:
Importing Emails via your FYI - My Imports folder in OneDrive
You can import historical emails by dragging and dropping them to your FYI - My Imports folder in OneDrive. These will be automatically imported to your In Tray. Emails imported from FYI - My Imports have a Delivery Status of "Imported". Refer to Using OneDrive FYI - My Imports to Automatically Import to your In Tray.
From your In Tray, update any details of the document(s), such as the Client and if needed the Cabinet and Categories. Then click File to file the document. You can use bulk update any documents that have the same filing details. Refer to Updating Filing Details of a Document and Bulk Updating of Filing Details.
Filing historical emails from Outlook
Alternatively, you can also file individual historical emails from your Outlook using the FYI Add-in. Refer to Filing an Email from your Outlook Inbox or Sent Folder in Managing Emails from Outlook.