5
phpmailer can handle sending html email. In XOOPS 2.5.5 you will need to hack the standard notification emails by modifying the ./kernel/notification.php file.
Somewhere around line 170 you should be able to add:
le="color: #000000"><?php $xoopsMailer->setHTML();
and then you will need to modify the template(s) to include the header, logo, etc. that you want and any html "improvements" you want to make to the template (
le="color: #000000"><?php <h2>, <b>, <i>
, etc...).