Hi
You can add the formats you like in the tiny_config.php of the Massmail module.
You have to add it to the tinyMCE.init() function, which starts at about line 87 in the tiny_config.php.
Here you can see the syntax:
es" target="_blank">http://tinymce.moxiecode.com/wiki.php/Configuration:theme_advanced_styl esI don't know if this is exactly what you want to have.
Best regards