I'm looking for alternatives to Yahoo Groups. I like the Yahoo Groups 
features of archiving messages, having a place to archive files, and 
being able to schedule events (with automatic reminders) on a calendar. 
Ranked features from most to least important are:

1. One email address which reflects to everyone on the list.
2. Closed list (only members can send email, joining list must be approved)
3. Calendar reminders

Nice, but not necessary:
4. File archives
5. Message archives

There are a few drawbacks of Yahoo Groups. First, I want to add/remove 
people to the list without the list member having to do anything 
special. Some of the members of my lists have email but are 
computer-challenged. Second, Yahoo Groups sometimes gets bogged down and 
timely messages (like calendar reminders) don't go out when scheduled.

My group of volunteers has no funding, so very cheap, preferably 
open-source suggestions are most appreciated.

Thanks!

-Jeff