HTML Mail lets you theme your outgoing messages the same way you theme the rest of your website.
The following additional modules, while not required, are highly recommended:
Also available as a patch.
Visit the Mail System settings page at admin/settings/mailsystem to select which parts of Drupal will use HTML Mail instead of the default mail system.
Visit the HTML Mail settings page at admin/settings/htmlmail to select a theme, pre-filter, and post-filter for your messages.
The email message text goes through four transformations before sending:
The Text format pre-filter from the module settings page is applied. This should be the same text format that your website uses for contributed content such as comments or blog postings. For consistency and security, it should include the the Correct faulty and chopped off HTML from filter.module, or a better replacement such as HTML Purifier or htmLawed.
A theme template is applied. The default template is the included htmlmail.tpl.php
file. You may copy this file to your theme directory and use it to customize the contents and formatting of your messages. The comments within the file contain complete documentation on its usage.
The message may be wrapped in a website theme selected on the module settings page. Creating an email-specific sub-theme lets you use the full power of the drupal theme system to format your messages.
The Text format post-filter from the module settings page is applied. For best results, this should be an email-specific input format containing the following text format filters:
Visit the issue queue for support and feature requests.
http://drupal.org/project/emogrifier
http://drupal.org/project/htmlpurifier
http://drupal.org/project/htmlawed
http://drupal.org/project/mailmime
http://drupal.org/project/mailsystem
http://drupal.org/project/pathologic
http://drupal.org/project/transliteration
D7: http://api.drupal.org/api/drupal/modules--filter--filter.module/7
D7: http://drupal.org/documentation/install/modules-themes/modules-7
http://drupal.org/documentation/theme