mbox is a generic term for a family of related file formats used for holding collections of electronic mail messages
All messages in an mbox mailbox are concatenated and stored as plain text in a single file. The beginning of each message is indicated by a line whose first five characters consist of "From" followed by a space (the so named "From_ line" or "'From ' line" or simply "From line") and the sender's e-mail address. A blank line is appended to the end of each message. For a while, the mbox format was popular because text processing tools can be readily used on the plain text files used to store the e-mail messages.
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