I haven't worked at sendmail or even anything e-mail related, and I can do that… just enough e-mail fixing as side work. Let's call it sysadmin calluses.

What made me stumble recently was having to talk LMTP to fix a mailman setup. Cheeky fuckers changed EHLO into LHLO for LMTP. (To avoid any mixups between the protocols, which is fair.)