OG och mail lists mailman
Webmail Plus is a full-featured email client for Drupal. It's designed to provide email for any or all members of a Drupal site. It relies on a standard IMAP (Dovecot, Courier-IMAP) server for mail storage and localhost or SMTP (Postfix, Exim) server for mail delivery. It's a great way to add email/webmail functionality to your Drupal community site.