mbox is a file format used for holding e-mail messages. In this format, the messages are concatenated with a From line added to the beginning of each, and a blank line is added before each From line except the first. The From line begins with the five characters "From ", and may continue with other text.
If the string "From " occurs at the beginning of any line in the body, it must be modified to prevent it being taken as a message boundary. This is typically done by prepending a greater-than sign.
