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sort

SORT  -  sort messages by date

Usage:  SORT

The SORT command sorts messages chronologically by the dates the
  messages were received on your machine.  In your main mail file,
  messages are already sorted that way.  However, if for example you 
  MOVE messages between mail files, they may become disordered, and 
  SORT will rearrange them.

For more help type "help" and one of these topics:
  headers   get   move   copy   filing
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