mark

MARK  -  mark messages as seen without reading them

Usage:  MARK [message-sequence]
  Unless specified, the message-sequence is "current".

The MARK command marks UNSEEN messages as SEEN.  It might be used to 
  prevent "read unseen" (implied by typing "read") from displaying 
  certain messages.

Examples:                    
    MM>mark unseen		#same as "mark all", marks all as seen
    MM>mark from stranger	#marks messages from "stranger" as seen

For more help type "help" and one of these topics:
  message-tagging   read   unmark   message-sequence   headers