Unix Mailbox — universal email archive format
MBOX (Mailbox) is one of the oldest and most widely supported email storage formats. It stores all messages in a single file, with each message separated by a "From " line. MBOX is the native format for Thunderbird, Apple Mail, and many Unix-based mail clients, making it the go-to format for cross-platform email portability.
Origin
Unix/Linux mail systems
Used by
Thunderbird, Apple Mail, Gmail exports (Google Takeout), Postfix, Dovecot
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