hmmnn I was thinking...
Many, many moons ago when I used to subscribe to newgroups which then was called UseNet, it was in my OE that I had the Mail or News option. That was the one I mentioned earlier ... Tools/Options/Send.
To send to usenet I had to make sure that my NEWS Options in my email programme (in my case back then it was outlook express) were set to Plain Text.
Now I know that Yahoo groups is different, but I'm still thinking that if the Yahoo Groups preferences are OK, then you need to check in your Verizon because there are two types of options in OE e.g, one for news and one for mail. Both have HTML or plain text options and advanced settings.
I would double check what Jo posted in post # 7
http://neurotalk.psychcentral.com/post452791-7.html