Sendmail was my first real project as I needed to get Sendmail 4 working on a LynxOS system (a real time Unix running on 386 hardware). Due to the lack of needed software libraries, I ended up having to turn on all these features listed as deprecated and work through how they worked. All the while getting email and encouragement ("I think it still works but man I really don't want to go there again") from an Eric Allman. I think it was after I had finished reading the Bat Book of 1990 that I realized they were one and the same.
Thanks Eric, for writing software that would allow me to do all kinds of crazy things (and for giving my professor a project of what compilers would compile to (.cf)