headers

HEADERS  -  display the header (one-line summary) of the current message

Usage:  HEADERS 

Please note that HEADERS acts on the "current message" in your mail file,
  and not on the outgoing message.  If you are REPLYing, the current
  message is the one you are replying to.

The HEADERS command shows a one-line display for the current message with 
  the sequence number, date, sender, subject, status and length.

In the display, the status letters at the left indicate the following:
  A:answered (replied to).  D:deleted.  F:flagged.  K:contains a keyword.
  N:new (unseen and recent).  R:recent (arrived during this MM session).
  U:unseen (never read).

For more help type "help" and one of these topics:
  basic