Junk mail/return encrypted-blo

[s.summers1 at genie.geis.com]

>From zane at genesis.mcs.com (Sameer)
 
>The second solution I thought of seems like it would work. When I
 >create the return-address block, it can be given some sort of ID-code
 >(again, like with my other idea posted, similar to the ID-code on peices
 >of Digicash in Chaum's scheme) so when the vendor delivers the product,
 >she sends to encrypted block to the remailer, and the remailer forwards
 >the product to me, and stores the ID-code in its database (doing the
 >proper one-way transformation for untraceability) so that further
 >attempts to use the exact same address-block will be noticed and not
 >delivered.
 
        Why not just include an Expire: header in the encrypted block, after
 which the remailer would just junk any mail sent with that return address?