What is the difference between “mailbox” and “folder”?
The term “mailbox” is IMAP-speak for what a lot of software calls a “folder” or a “mail folder”. However, “folder” is often used in other contexts to refer to a directory, for example, in the graphic user interface on both Windows and Macintosh. A “mailbox” is specifically defined as a named object that contains messages. It is not required to be capable of containing other types of objects including other mailboxes; although some mailbox formats will permit this. In IMAP-speak, a mailbox which can not contain other mailboxes is called a “no-inferiors mailbox”. Similarly, a directory which can not contain messages is not a mailbox and is called a “no-select name”.
