The program is located in /usr/bin/mail.  Upon execution, Version 8.1.2 01/15/2001 is shown.Entering list produces:Commands are:next, alias, print, type, Type, Print, visual, top, touch, preserve, delete, dp, dt, undelete, unset, mail, mbox, pipe, |, more, page, More, Page, unread, Unread, !, copy, chdir, cd, save, source, set, shell, version, group, write, from, file, folder, folders, ?, z, headers, help, =, Reply, Respond, reply, respond, edit, echo, quit, list, xit, exit, size, hold, if, else, endif, alternates, ignore, discard, retain, saveignore, savediscard, saveretain, core, #, inc, newEntering ? produces:Mail Command               Description-------------------------  --------------------------------------------t [message list]           type message(s).n                          goto and type next message.e [message list]           edit message(s).f [message list]           give head lines of messages.d [message list]           delete message(s).s [message list] <file>    append message(s) to file.u [message list]           undelete message(s).R [message list]           reply to message sender(s).r [message list]           reply to message sender(s) and all recipients.p [message list]           print message list.pre [message list]         make messages go back to /var/mail.m <recipient list>         mail to specific recipient(s).q                          quit, saving unresolved messages in mbox.x                          quit, do not remove system mailbox.h                          print out active message headers.!                          shell escape.| [msglist] command        pipe message(s) to shell command.pi [msglist] command       pipe message(s) to shell command.cd [directory]             chdir to directory or home if none givenfi <file>                  switch to file (%=system inbox, %user=user's                           system inbox).  + searches in your folder                           directory for the file.set variable[=value]       set Mail variable.Entering z shows the end of the list of messages - but that command is not presented in the ? help page.What program is this?Are there tutorials for its use?What are some common commands and helpful tricks for its use?How can the message list be navigated (the opposite of z) or refreshed?Clarification: This question is about the interactive program and not the script-able command - i.e. the result of typing mail with no flags or parameters into a terminal.
What is mail, and how is it navigated?
linux;mail command
This page describes the interactive command in detail, and is in fact a fairly thorough tutorial. Describes commands such as z and z- :If there is more than a screenful of messages, then z willshow the next screenful, and z- will show the previous screenful.Hope that helps.