I do not know if it is possible to use UE with Yahoo webhosting. I think your best bet would be to contact your technical support for the hosting and ask them about the specific scenario you have.
Essentially you will need to know if you can use a php mail call within your scripts and if so you should request and example script. If you can post back with this we should be able to take a look to see if you can use UE for this. Here is a link to the mail page on the php site:
php.net/manual/en/function.mail.php
