My mother in law needs to email several hundred people a few times a year as part of a volunteer art society email newsletter. She was going to use her Hotmail account and just BCC everyone, with a backup option of doing the same thing with the email I host from her on her domain (HostGator). I think there are two problems with either approach:
 - Spam filters could bin most of the emails
 - It could mark her account as spam and have it closed

Is there a decent, free way to do this? It must be mother in law proof, because I don't want to spend hours and hours working on this. I could for example install email list manager software on her domain, but the free stuff tends to be complex. They just want something simple - perhaps some kind of proxy that accepts a single email and distributes to a predefined list?

Oh, and of course, it needs to be free since it's a volunteer society.