I know this question is a bit vague for SO, but I'll try to get it to the point: I want to get a better understanding of mail servers and the SMTP protocol. There are quite some products (sendmail, postfix, exim, ...) with HUGE documentations. And there are RFCs. But is there something in between? Some overview how real world mail sending and retrieving works?
I think about setting up my own mail server (or even implementing one using twisted), but my feeling is, that all those products solve problems I don't even know they exist. But I don't just want to install some software. I want to understand what's going on. Where do I start?