The mail program uses several files. They are:
/usr/spool/mail/Mail.rc The global start-up file from which the mail program gets its default values.
~username/.mailrc A personal start-up file in your home directory. You have to create this file and its contents.
~username/mbox The file in your home directory where your mail is stored once it has been read.
~username/dead.letter The file in your home directory where any mail message that you decide not to send is stored.