Hi - > Such a service is not currently available on sourceware, but it'd be > possible to implement: as messages come in, you'd build a database > mapping from the Message-ID header to "current Mailman's Pipermail URL".
I was thinking we might be able to trick pipermail (the web archiver component) to simply name the message web urls after some function of the message-id instead of the sequence number. Will give this a try very shortly. - FChE
