how to check incoming mail per Date field

I would like to set up my procmailrc to save 
yesterdays mail to DATE.mbox.  I came up with the
variable CURRENT_DATE='date +%a, %d %h 19%y'.  Will
the following sort yesterdays' mail to DATE.mbox?:

CURRENT_DATE='date +%a, %d %h 19%y'
MBOX_DATE='date +%y%m%d'

:0
* ^Date:.* < CURRENT_DATE
$MAILDIR/${MBOX_DATE}_mbox


Reading the PROCMAILEX(5) yielded nothing directly related

Thanks in advance
danielt(_at_)susq(_dot_)com

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