I assume that your friend (the recipient) is using BT.Yahoo on her desktop, i.e. she is '''not''' using an email client like Thunderbird. If so, her machine should display correctly an email that is sent in html format, since it is in effect displaying a web page. So look at your settings under Preferences > Composition > General. Under 'HTML' specify the font you want to use '''and the font size'''. (Mine is set to 'large'.) For added assurance, click on the 'send options' button and add your friend's address to the domains specified to receive html -- that should guarantee that she receives it in the correct format. If you know that she is receiving an email sent in html format with the font size set to large, and it's still displaying in a tiny font on her machine, then the problem is at her end I'm afraid.