One elaboration on the comments Ned made (with which I agree):
--On Monday, May 31, 2004 09:59:27 AM -0700
Your diagram implies scenarios such as delivering into the MS by imap
and then having the MUA access the MUA by pop. Do we really want to
It is not all that uncommon for IMAP append to be used to deliver
messages to a store. For example, suppose you have an MTA that performs
final delivery using LMTP and you want to use it with an IMAP server that
doesn't support LMTP delivery. The obvious thing to do is write an LMTP
server that stuffs messages into the IMAP server using APPEND.
Its worth noting that many message stores provide both POP and IMAP access
simultaneously, so its quite possible to have message delivery into the
store via IMAP APPEND and MUAs using POP (or IMAP) to read the messages.