Official would be set up by the club, or officially sanctioned with
the club. An official group would have some sort of contract with the
Houston Astros, and would almost certainly be linked to at
astros.mlb.com. It really bugs me when some random Joe Schmoe sets up
a website or a club and calls it "official".

I'm sure this is a great group, but it isn't official, and the name
is very misleading and deceitful.

The most active Astros group at Yahoo!, with 20 posts this month
alone (April), is Houston's Brand of Baseball at
http://sports.groups.yahoo.com/group/houstonsbrandofbaseball/. It had
84 posts for the month of March, 104 in January, and 197 last
October. There's a diverse cast of characters around; those posts are
coming from quite a few different people. No, it's not official, but
it doesn't pretend to be. It's just large, active, and fun, so come
check it out!
http://sports.groups.yahoo.com/group/houstonsbrandofbaseball/