All command-line arguments that follow the switches (if any) are
taken to be the addresses of recipients.
The addresses in the list may be separated by spaces,
by commas, or by both:
addr1 addr2 addr3
addr1, addr2, addr3
Certain modes specified by the
(for print the queue's contents), cause
to ignore any list of recipients.
Be sure to escape any characters in addresses that
have special meaning to your shell. For example, because the
character has special meaning to the C-shell,
it should be escaped by preceding it with a backslash character:
expects a list of recipients and finds none,
it prints the following message and exits:
Recipient names must be specified