It's a Yahoo group. They suck, big time. Worst user experience of any discussion medium on the 'net. The problem is they don't have *anyone* in their employ who understands communication.
[Watch out, I'm on a RANT]
They don't allow or understand plain-text, even with the email option.
They don't provide any mechanism for threading, even with the email option.
The email option breaks so many RFCs that it should be arrested as a war criminal, and yes, I know the apparent disparity in description. There is no disparity.
Yahoo! for groups is as AOL was for Usenet. Remember the everlasting September?
http://en.wikipedia.org/wiki/Eternal_September
Thankfully now over since AOL has withdrawn Usenet access from its captives.
[Rant suspended for now]