from —
print names of those who have sent mail
  
    | from | [ -ssender]
      [-ffile]
      [user] | 
from prints out the mail header lines from the invoker's
  mailbox.
Options:
  - -ffile
- The supplied file is examined instead of the invoker's mailbox. If the
      -foption is used, the user
      argument should not be used.
- -ssender
- Only mail from addresses containing the supplied string are printed.
If user is given, the
    user's mailbox, is examined instead of the invoker's
    own mailbox. (Privileges are required.)
The from command appeared in
  3.0BSD.