Yes you can send HTML e-mails with Yahoo.
Is Sentvia a MLM company?
Check out
Constant Contact if you're sending a lot of e-mails.
Their system actually recognizes if the recipient can handle an HTML e-mail and will revert it to a text e-mail if needed. So it sends both out. People can even request to receive text only when they sign up for your list.
You always have to remember, not everyone can receive HTML.
They also have a 60 day free trial. If you are below 50 subscribers it's free and the price is graded after that. So it's perfect for someone just starting out.
I use Constant Contact for everything and it's worked flawlessly.
I hope I've helped!
Good Luck,