undelete

UNDELETE  -  remove the mark for deletion

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

The UNDELETE command removes the D indicator from the header line of
  a message.  The D shows that you marked the message for deletion with 
  the DELETE or MOVE command.  If you change your mind, you can UNDELETE 
  the messages.

When you use the EXIT or EXPUNGE commands, messages marked for deletion
  will be permanently removed.  You cannot undo that.  

Example:
    MM>undelete 16

For more help type 'help' and one of these topics:
  delete   move   message-sequence   exit   expunge   message-handling