The remailer could calculate a hash for the body of each encrypted message received (the same portion which will be decrypted by PGP), tabulate the last few thousand hashes, and simply discard any messages with a duplicate hash. The target of the attack would receive only the first copy of the message.
That wouldn't keep the mailer from getting choked up pretty quickly, though, especially if it's on the end of a < T1 line. -- Ed Carp, N7EKG Ed.Carp@linux.org, ecarp@netcom.com 214/993-3935 voicemail/digital pager 800/558-3408 SkyPager Finger ecarp@netcom.com for PGP 2.5 public key an88744@anon.penet.fi "Past the wounds of childhood, past the fallen dreams and the broken families, through the hurt and the loss and the agony only the night ever hears, is a waiting soul. Patient, permanent, abundant, it opens its infinite heart and asks only one thing of you ... 'Remember who it is you really are.'" -- "Losing Your Mind", Karen Alexander and Rick Boyes