Opening htmls on Iphone using Yahoo

I created an html in Dreamweaver and it looks fine in MS Outlook, but when someone opens it on their iphone, it doesn't display properly. It is very tiny and only shows up on the right hand side of the screen and there is no way to diplay the email properly. I've had my techie look at this, and he can't figure it out. It displays ok on a Blackberry. Is there a setting in Yahoo I have to change that will make emails display properly?

What's funny is when someone forwarded the email to me and I opened it on my phone, it first looked tiny, then popped up correctly. But when it is sent directly, it doesn't do this.

Can anyone help me? I'm about ready to blast a group of brokers an open house invitation, and most people open with their smart phones, so I want this to look right.

Thanks for your time and support!