Contact Form 7 Group Mail allows you to send messages to multiple users, according to their groups. With this plugin you can choose who (admins, editors, authors, contributors, subscribers and custom roles) are going to receive the e-mails.
The list of recipients is automatically updated, so it’s not needed to change the contact form every time a user is added or removed.
Important: it is an extension for Contact Form 7 plugin.
This plugin is available for download to be used on your WordPress self-hosted installation.