I’m afraid I know nothing about ‘Becky’ and ways/methods to export from within it, but if you can export the messages as .eml files to a folder, you should be able to drag the msgs from that folder either singularly or in bulk to an Outlook account Inbox of your choice.
They are then viewed like any other msg in an Inbox or other folder.
Alternatively, the saved/exported .eml files in the folder should automatically open when d/clicked in Outlook if Outlook is set as the default email client. This, perhaps, is a preferable way to avoid ‘clogging’ up Outlook with msgs that are no longer of great importance but can still be accessed via the folder that contains them should they want to do so.