So you’ve converted all you mail and imported into your new email app and everything looks fine. But when you open up one of your old sent folders and you see a list of messages that show the From column instead of a To column.
Your new email app doesn’t know that your old sent mail folders are sent folders, that’s all, and it’s easy to fix. Just change the view options or column settings for those folders to show the Recipient (or To) column instead of the Sender (or From) column.