You
can use the Mass Mail feature built into Joomla:
http://docs.joomla.org/Help32:Users_Mass_Mail_Users
But I wouldn't!
It's a quick way to get your IP address debarred for spamming. Many ISPs do not like mass mail being sent from their servers, or to their customers from untrusted servers.
You are much better off using a service like Campaign Monitor or Mailchimp for this.
EasySocial 1.2 includes a Mailchimp custom field, so you can use that to allow members to opt-in to your mailing list (very important).
Mark said he will look into adding the ability to allow users to subscribe to Mailchimp groups, which will make the feature much more useable.