WPMU DEV HTML EMAIL TEMPLATES Plugin
Add a HTML header and footer to the emails that WordPress generates.
WPMU DEV HTML EMAIL TEMPLATES Plugin allows you to use your beautiful HTML email templates for emails WordPress sends.
By default, WordPress sends out plain boring email notifications for events such as new comments, comments in moderation and new users.
Spice Up System Notifications
This plugin is for any brand-freak that loves completely white-labelled products, or for those who just want WordPress to send nice emails.