If you are receiving a GNU mailing list named `XXX', you might be able to unsubscribe to it by sending a request to the address `XXXfirstname.lastname@example.org'. However, this will not work if you are not listed on the main mailing list, but instead recieve the mail from a distribution point. In that case, you will have to track down at which distribution point you are listed. Inspecting the `Received:' headers on the mail messages may help, along with liberal use of the `EXPN' or `VRFY' sendmail commands through `telnet <site-address> smtp'. Ask your postmaster for help.