mail [recipient email address] The program will ask for a subject line, and then you can begin writing your email. Type Ctrl+D when you're finished writing to send the email. Type "~e" or "~v" on the next line to open an editor if you make a mistake and need to edit the email.
While composing an email, typing Ctrl+C will interrupt it if you decide you don't want to send. Type Ctrl+C a second time to exit the mail program and the aborted letter will be saved in a file called "dead.letter"