Install these modules
Provides Newsletter functionality, like subscription blocks, newsletters as content type and a sending mechanism.
Enables HTML emails to be send with simplenews. Also has important functionality like producing inline CSS styles via referened classes: define your styles via classes for develment and before sending those styles are made inline - great!
IMPORTANT: take care the style block in your mimemail-message.tpl is exactly as in the default template, otherwise the regex might not find the styles :/
Enable the minemail_compress submodule for this. Also supports base64 encoding of images.
Use an SMTP server for sending the mails. In contrast to the SMTP Drupal module, this one integrates nicely with mimemail.