Milter-greylist

I make use of plussed addressing as this allows me to have the wildcard 
address turned off in sendmail but lets me have supplier specific 
addresses.  But there is a problem.  I have just ordered some tickets 
using alan+ticketsupplier@... and am now waiting for the 
confirmation email - the log tells me it has tried and already hit the 
greylisting.

So what I would like is some form of time limited automatic whitelisting. 
I want it to be automatic so that I don't have to presetup anything for 
specific addresses but time limited so that it reverts to normal 
greylisting operation for when the addresss is released to the spam 
community.

As an example, if I used alan+20071007@..., it would be useful to 
configure greylisting to be bypassed for, say, a couple of days after the 
embedded date.  Or even better, to be able to use 
alan+20071007ticketsupplier@...

If this is not a suitable suggestion for including into the greylist 
program itself, is there a facility to run an external program such that I 
could parse the address for a date myself?

-- 
Alan


( Please do not email me AS WELL as replying to the list.  Please
   address personal email to alan+1@ as lists@ is not read. )