Mail format created for organizing and storing e-mail messages in a single text file; originally used by Unix hosts to store e-mail messages locally; messages saved in an MBOX file are concatenated one after another, starting with the "From" header.

Apple Mail 1.x (included with Mac OS X) saved messages in MBOX files and stored them in the /User/Library/Mail/Mailboxes/ folder. Apple 2.0 and later uses .EMLX format, which separates the messages into individual files so they can be searched by the Spotlight program.

The MBOX mail format is still used by several other e-mail programs, including those listed below.