MH and xmh - e-mail for users and programmers (2. ed.). - Jerry D. Peek (O'Reilly, 1993)

MH and xmh - email for users and programmers (3. ed.). - Jerry D. Peek (O'Reilly, 1995)

What you need to know using email effectively. - Linda Lamb; Jerry D. Peek (O'Reilly, 1995)

Learning Unix for Mac OS X - includes quick ref card. - Dave Taylor; Jerry D. Peek (O'Reilly, 2002)