The lab creates users alice and bob (password Lab-Pass-1). alice stands in for you: log in as her (or sudo -iu alice) to send and read her mail. No MTA should be installed yet; the lab refuses to start if one is. Reset removes Postfix and the mail client again.

Tasks

Install Postfix and choose "Local only" (Debian, Ubuntu), or install it and start it (RHEL family), so it listens only on this machine. Install a mail command too.
As alice, send yourself a message with the subject Hello me using mail -s, and read it with mail. Find the mailbox file in /var/mail.
Alias root to alice, run newaliases, send mail to root, and check it arrives in alice's mailbox.
Create a ~/.forward for alice that sends her mail to bob, and test it. Then change it to keep a copy for alice too, and send her another message.
Run mailq and sendmail -bp and compare. Find the sendmail command's real program with readlink -f /usr/sbin/sendmail, and write that path to /root/lab-answers/5.

Hints

The mail client is s-nail on the RHEL family and mailutils on Debian and Ubuntu. sudo dpkg-reconfigure postfix asks the questions again. postconf inet_interfaces.
mail -s "Hello me" alice; mail reads, q quits (read messages may move to ~/mbox).
/etc/aliases, newaliases; postmap -q root lmdb:/etc/aliases (or hash:) shows what Postfix sees.
\alice, bob in /home/alice/.forward, owned by alice, mode 644.