greylisting and MAIL FROM signing

I have run into a sort of impedance mismatch between MAIL FROM signing and 
greylisting.  

1. I send a message with signed MAIL FROM (old SES)
2. recipient rejects with 450 - try again in 300 minutes
3. sendmail tries again, but the timecode has changed, and so
   the recipients greylisting software thinks I'm a new sender.
4. go back to step 2

One solution would be to bind the MAIL FROM to the message somehow
when deferring due to 450.  But how to do that with sendmail?  I 
am signing MAIL FROM via a socket map - which is called on each attempt.
How would I recognize that it is the same message?  How could I get 
sendmail to keep the new MAIL FROM?

A real klugy solution would be to relay through another server - that's
one way of making the MAIL FROM persistent...

-- 
	      Stuart D. Gathman <[email protected]>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flamis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.