Hyperlink underlines and custom fonts

Hi all

I wonder if you could help me out.

I have two issues: one being the removal of underlines on hyperlinks and the other being using custom fonts.

I have an ePub file that works fine and looks exactly as it should. However, when I convert to mobi through the Amazon previewer, the underlines are re-introduced and the custom fonts fall away.

Does anyone have any suggestions for what I should check?

Thanks in advance
Dan