abredt said:
I am using Office 365 and its included Outlook 365 for emails.

I would like to back emails up to a USB drive. How do I do that?

Thanks, cb
Are you using Outlook 365 within a web browser or do you have the Outlook program?

If the former then your options are limited as discussed. I would use a free email client program from where you can select blocks of messages and save them to a location of your choice. I use Outlook 2010 / 2016 on my PCs and can easily store any message in various formats. You can also drag and drop messages to any drive.

Note if you configure your emails to use an IMAP server then copies of your emails should always reside on the server and be synced with the mail folders on all of your devices.