GET  -  go to another mail file

Usage:  GET [filename]

The GET command brings you to another mail file.  All MM commands then 
  apply to that file.  Other mail files can be created with the
  commands MOVE, COPY or WRITE, or by sending mail to a file (using an FCC
  field, for example).  The mail file you are reading now is your
  "current mail file".

If you do not specify a directory, GET assumes the one set by MAIL-
  DIRECTORY, which by default is your home directory.

GET with no filename always returns you to your main mail file, set by
  MAIL-FILE, which by default is "mbox".  

EXAMINE is similar to GET, but retrieves the mail file in
  read-only mode so that you cannot accidentally change the file.

For more help type "help" and one of these topics:
  examine   copy   move   filing   cd   write
  set mail-directory   set mail-file