Which mail do you want to import?
Mail saved by a desktop client: a Thunderbird folder, an Apple Mail export, a Gmail Takeout .mbox, or .eml files. It is read in this browser and goes straight into the new mailbox; we never store it.
Drop a folder or mail files herembox files (Thunderbird, Apple Mail, Gmail Takeout) and .eml files
Where to find them: Thunderbird, Apple Mail, Gmail Takeout. Outlook .pst files go through the free CLI, which also suits thousands of files or many GB.