utf8 iso-8859-1 hotmail characters

Hi, I work with Spanish language, and sending mail to hotmail or any account received by Outlook
characters such as accent or letter ñ are destroyed. there is no way to make htmlmail mail to send mail to hotmail accounts encoded in the iso-8859-1
With gmail account works fine, but not when they are received by Outlook or thumderbir
There is a solution for this problem?

Thank you