Offer your Mambo/Joomla users free email forwarding using their Mambo usernames. All of your users will automatically receive an email address like: username@yourdomain.com. When someone sends them email, it will forward it to the email address they registered with when they signed up.
This is the lite version of Mambo Mail Pro, which offers many more features. Please read the Readme file before you install.
Download here.