You can export your email archive using the following options
This is used to export all of your emails in MBOX format. MBOX format is very common email archival format. This can be used to import mails to email clients like Apple Mail, Thunderbird etc. Here’s an article from Mozilla detailing the approach.
You can use this option to export you emails in a ZIP format. It is simply a package of your emails in .eml format. It can only be used with Horcrux Email backup. The advantage is, it is a much lighter than an mbox file (as it doesn’t have duplication from multiple mailboxes).
Internally, Horcrux Email Backup stores emails as .eml files. You can use this option to view the files.