How to use HTML tags in email?
Check out Mime Mail; that should do the trick.


  This is a Mime Mail component module (for use by other modules).
  
  
  It permits users to recieve HTML email and can be used by other modules. The mail functionality accepts an HTML message body, mime-endcodes it and sends it.
  If the HTML has embedded graphics, these graphics are MIME-encoded and included as a message attachment.
  Adopts your site's style by automatically including your theme's stylesheet files in a themeable HTML message format
  If the recipient's preference is available and they prefer plaintext, the HTML will be converted to plain text and sent as-is. Otherwise, the email will be sent in themeable HTML with a plaintext alternative.
  Allows you to theme messages with a specific mailkey.
  Converts CSS styles into inline style attributes.
  Provides simple system actions and Rules actions to send HTML email with embedded images and attachments.