A few days ago I signed up for some SF mailing lists from Yahoo groups, but I’ve yet to see a single message from any of them.
Anybody here subscribe to a decent SF mailing list? How much traffic does it generate?
Try this one – Yahoo | Mail, Weather, Search, Politics, News, Finance, Sports & Videos – 2 new members and 50 new messages in the last 7 days. That’s busy enough for me, might not be for you.
Have you been to the SFF World message boards? They have a science fiction forum as well as author forums. Science Fiction and Fantasy World
The Yahoo Groups mantra is “If it’s too quiet for you, then start something.” 
When a group has been together for awhile, things slow down, and it takes some imaginative moderating to get discussion going.
On second thought, it’s weird that you joined several groups and haven’t seen any messages. Maybe it’s a Yahoo problem.
Has your membership been approved by the moderators?
Well, there’s no indication in the welcome emails I got that my membership is pending approval, so I don’t think I’m waiting on that.
FWIW I joined
science_fiction_fantasy
Science-Fiction-Writers
Science_Fiction_Short_Stories
and actually I see now I only signed up yesterday, it only seemed like a few days ago. Still, zero messages from three groups even in just one day is pretty quiet.
I’ll give those two you mentioned a try, thanks much!