I want to elaborate on Eric's comment about the "##" pasting token. The cypherpunks remailers are activated by mail header fields. They look for a header entry of the form "Request-Remailing-To:" among the Subject, From, To, etc. headers. Although it is traditional for user-defined extension header fields to start with "X-", Eric argued that since we hope to extend remailer availability to the point that it is a widespread and standard service, it was reasonable to choose a non-"X-" field name. Since some mailers don't allow users to insert header fields, Eric created the "::" incoming pasting token. If no header field is found matching the ones the remailer looks for, it then checks to see if the first non-blank line of the message is "::". If so, it copies all the following lines of the message into the header, up to the next blank line, and then restarts processing of the message. The "::" line is intended to be followed by the user-added header fields like "Request-Remailing-To". When the remailer does a remailing step, it strips all of the header fields except Subject. Keeping the Subject header impairs security somewhat because it would facilitate pairing up input and output messages, but it adds a lot of convenience for users. What is little known is that there is another step which can be done. Just before the remailer sends a message for which remailing has been requested, it again checks the first non-blank line, this time to see if it is the outgoing pasting token "##". If so, it again copies the following lines up to a blank line into the message header of the outgoing message. The message is then sent without further processing. This means that any header line can be added to an outgoing message by this means. In particular, as Eric pointed out, a Reply-To header could be added which would reveal the true sender of the message for those cases where that was wanted. Subject headers could also be added at this step as well as after the :: incoming pasting token. Hal Finney hfinney@shell.portal.com