Just to try to explain my own components to Joe.

fetchmail: This does what it says. It (periodically) fetches mail from our external email accounts and hands it over to...

postfix: This is what is known as an MTA (mail transfer agent). This moves mail around. For my usage, it delivers the mail to...

cyrus. This is an email (IMAP/POP) server. This is where the individual mailboxes are and where the PCs, Androids, etc. see the email from.

(ours actually goes through span and virus filtering in the chain but the above gives the general idea)

There are other ways of working with these types of components.

I could set postfix up to send mail to others. But non business IP addresses tend to wind up on blocks of blacklists (I think it is assumed home users should not be sending mail and most email originating from such an IP address is the result of a hacked computer). That and I believe spammers are always on the look out for insecure SMTP servers...

It would be possible for me for example to direct incoming mail straight to my folkinfo domain address rather than have it go to my ISP and have fetchmail, hmm fetch it from there. On the plus side, that would cut out the few minutes lags between fetchmail checking for mail.

One could make a full blown email system or (as I do) just make use of some bits.