mail01
Test that mail user@domain will send a mail to that user at that domain.
mail02
Test that mail user@bad-domain will result in a warning from the mailer daemon that the domain does not exist.
mail03
Test that mail non_existent_user@localhost will result in delivery failure. Mailer-Daemon will report this failure.
mail04
Test that mail -c user@domain option will carbon copy that user.
mail05
Test that mail -b user@domain option will blind carbon copy that user.