Re: playback attacks on PEM?

   >>       Also, as Steve Crocker points out, use of any sort of message
   >> ID, covered by the PEM protection, will suffice to detect replays.  The
   >> use of sequence numbers also allows a recipient to detect deletions
   >> as well.
   >
   >Why not simply a date.  It won't prevent deletions, but replays
   >become irrelevant.
   >
   
why do you trust the source of the date? can  this not be spoofed?