I'm not sure you get invited so much as automatically put on ;) The emails arrive when Mark has something to tell us. It could be a job hunting event for disabled or dyslexic people, or information about a new piece of assistive tech (like this one), or a link to a site to protest about some major body doing something clueless or discriminatory, or the manifestoes of people standing for Disabled Students Officer.

Everyone on the list gets all the emails, on the basis that you might have disabilities that you haven't disclosed or friends with the disability who haven't contacted the Disability Office. I found that annoying at first, but I've since realised it can be useful. I suppose the emails come every couple of weeks on average.