Just upload your MBOX files. You will get compressed archives instantly.

What type of file is MBOX?

MBOX (sometimes known as Berkeley format) is a generic term for a family of related file formats used for storing collections of electronic mail messages. MBOX formats store all of the messages of an entire folder (not an entire mailbox) in a single database file and new messages are appended to the end of the file.

Can Gmail read MBOX files?

In the context of Gmail, the “Download your data” function downloads the file in the MBOX format. ... However, using readily available third-party tools for free, but you can also import MBOX to Gmail and have access to the emails contained in the MBOX backup.