Mbox is a generic term for a family of related file formats used for holding collections of email messages.
All messages in an mbox mailbox are concatenated and stored as plain text in a single file.
As a specific example, if exporting via IMAP the popular Gmail service uses - as a placeholder in lieu of the sender's address, follows this with a timestamp representing either the time the IMAP export was configured or the time of reception (whichever is more recent), and makes no attempt to escape "From -" strings which appear in the body of an email.
mboxrd was invented by Rahul Dhesi et al. as a rationalization of mboxo and subsequently adopted by some Unix mail tools including qmail.
All these variants have the problem that the content of the message sometimes must be modified to remove ambiguities, as shown below, so that applications have to know which quoting rule has been used to perform the correct reversion, which turned out to be impractical.
Various mutually incompatible mechanisms have been used by different mbox formats to enable message file locking, including fcntl() and lockf().
In open source development, it is common to send patches in the diff format to a mailing list for discussion.
[8][9] Version control systems like git have support for generating mbox-formatted patches and for sending them to the list as emails in a thread.