[Dovecot] What would you tell the CIO in an "ABCs of Email" overview?

[Kenneth Porter]

Perhaps the first fundamental is that Internet email isn't handled by one 
kind of server. It's a suite of protocols that are served by distinct 
processes.

At minimum, you have inbound (POP3, IMAP) and outbound (SMTP) servers. You 
may also have a separate authentication server (LDAP) and perhaps other 
pieces providing calendaring, web mail (HTTP), and central storage of 
client configuration (ACAP).

The different protocols exist not because some programmer thought it would 
be cool to create a new protocol, but because they serve completely 
different needs. For example, POP3 was designed to support lightweight 
disconnected clients. IMAP provides server-based storage of mail folders. 
LDAP provides authentication not just for mail systems but for many other 
applications. (I'm sure experts for each of these protocols could provide 
better explanations. The RFC for each probably has a motivation section 
that you can quote.)

An important "slide" in the presentation would show the plumbing that ties 
all these protocols and processes together and shows how mail moves through 
the system. In some cases the plumbing itself is variable. For example, 
spam and virus processing might occur within several servers or within a 
client.