Encore une fois je ne pars pas de Berkley/Unix, ni de mbox, ni de maildir, ni de procmail, mais bien de thunderbird et c'est ma douleur...

Thunderbird, Netscape, Mozilla Suite and SeaMonkey use mbox files to store the messages for a folder. The ImportExportTools extension can import and export mbox and .EML files. Many email clients use mbox files (regardless of whether they use no file extension, .mbx or .mbox as the file extension) to store messages or provide a way to export folders as mbox or .EML files due to the popularity of Eudora and Outlook Express. Sometimes email clients use "Unix format" to refer to a mbox file since the format was originally developed for Unix systems.