Modules: Webform and Mimemail - How can I edit HTML-Emails in Webform through a WYSIWYG Editor

Hi everybody,

I wonder how one can send HTML-Emails through webform using a WYSIWYG-Editor in the "Edit E-mail settings"?
I installed Mimemail, but the textfield of the E-mail template remains as it was before: a simple textarea without any formatting options (like I have for simplenews or all regular nodes and article pages).

How can I activate this?

Thank you for any help!

Bests,
Soezkan