flag

FLAG  -  mark a message so it stands out

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

The FLAG command puts a "flag" or marker on a message.  The letter "F"
  appears next to it in the header line.  By default, when you start
  up MM you see headers of flagged messages as well as new ones.  You
  can also use "flagged" as a message-sequence.

Examples: 
    MM>flag 3		#flags message 3
    MM>fl subj urgent	#flags messages with "urgent" in the subject
    MM>read flagged	#reads flagged messages

The UNFLAG command will remove the flag.

For more help type "help" and one of these topics:
  message-tagging   unflag   message-sequence  headers   
  set display-flagged-messages