... e-mails.When spammers use infected computers of unsuspicious users, e-mails maybe sent on behalf of the user, thus exploiting the user s ESP.Organizations which send solicited bulk e-mail, e.g. ... by his or her user- name, with the policy part given as the extension, as in a user+ extension”convention. Since presumably the “naked” (with no extension) main addressof the user would still ... generated, usinga user- specific (symmetric) key, will the SPA block be user- specific.2. The SPA block is encrypted under a symmetric key (256 bit AES-key inCBC mode) known only to the user creating...