I think can still do it, 30 years after I last had to. The trauma of debugging sendmail m4 config issues for hours while the company e-mail remained dysfunctional has permanently etched it into my mind.

  EHLO example.com
  MAIL FROM:<foo@example.com>
  RCPT TO:<bar@example.com>
  DATA
  Subject: Hello, World

  I have crawled through the depths of hell to deliver unto you this message.
  .

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.)