I tried to learn Sendmail when I registered my own domain and set up a server in 1995. My requirements weren't that complicated, but I never good get it to work the way I wanted, even with help from the guy that maintained the Sendmail configuration at my day job. I went looking for a "Sendmail for Dummies" book, but of course there isn't one, and I later realized that expecting one is about like expecting to find "Quantum Chromodynamics for Dummies".
I switched to Qmail, and had no trouble getting it to do what I needed. More recently I switched from Qmail to Postfix.