This part will give the definition of some objects.
A message is the common e-mail message or news message you read or send.
A message can have attachment such as images or other documents. The attachment are organized into a tree structure. Each node of this structure is a MIME part.
A mailbox will contain a given number of messages.
A storage is a "physical" localisation of your mailbox. This can be on a filesystem (local or remote disk, this is the case of MH, mbox and maildir), or this can be on a remote host (this is the case for POP3, IMAP or NNTP).
A storage, for the same user, can contain a given number of mailboxes, depending the storage capabilities, then, the storage driver capabilities. With etPan!, MH, IMAP and NNTP storages can have more than one mailbox. The mailboxes will be called folders. On storage where we only have one mailbox, the unique mailbox is the unique folder.
The session is the network connection or the entity to which the commands of the drivers are given.