> I need some help thinking about this - Pop and IMAP handle incoming
> mail for MUA
... after the MTA has received it and placed it in a store which is made
available by POP3 or IMAP, yes.
> However,
> what are the parts when all-z you want to do is webmail? So, my
> users will send and receive all mail via web.
You need a system which accesses the mail store (e.g. via POP3 or IMAP)
and presents their content to the user via Web. Conversely, that system
will have some sort of form which allows users to send a message.
Systems that come to mind are Squirrelmail [1] or Roundcube [2], but
there are others.
-JP
[1]
http://squirrelmail.org/
[2]
http://roundcube.net/