[Mailman-Users] bogus subscription requests

[editor at visionscience.com]

I maintain a few lists using Mailman. Everything works fine. Except that with some regularity I receive subscription requests for the list Mailman at myserver.com <mailto:Mailman at myserver.com>. The messages announcing the requests offer me a link to process the request. The link yields a 404 error message.
So far as I know, no such list exists.
When I check the overview of my lists, it is not among them.

I am aware of the concept of a sitewide list, and maybe this is that. 
But the question is: how can I reject these subscription requests, or can I just ignore them?

Using Mailman version 2.1.23