You could construct a file with a text editor, save it, and then send
it as the body of a message.
To send the ASCII file named a01 to a user named p373 use
mail p373 < a01
Rather than taking the message from the keyboard, in this case the
mail utility takes its input from the file a01, as specified by
the Unix redirection sign <. Note that the file comprises the
entire message. This procedure does not fill in a subject field for
the file. To do that you must use the variant:
mail -s "Assignment 1" p373 < a01
The subject field for the generated message is Assignment 1.
Please be sure to enclose the text of the subject field with quotes.
Note: Not all mail versions understand the -s option.