Mauricio - 8:38 am on Jan 21, 2004 (gmt 0) Due to the email specifics, maybe advertisers could opt-in on this system.
I've read that Google has registered googlemail.com and maybe the easiest solution is:
a) Google launchs an email list service and the Adsense publishers must open an account there
b) The publisher sends the email to the list server and there the message is readed and the plain HTML tags are included with the adequate advertisers.
Due to the email specifics, maybe advertisers could opt-in on this system.