I have done complete Joomla web-application with component for mailing newsletters to users, with these capabilities:
E-mail validation and confirmation
Automatic synchronization with your Joomla Users
Subscription opened to non-logged in users
Import Users from any source
Export users in CSV
I am able to demonstrate it to you, providing a link to my demo site, and temporary admin access, you can test it, and if you will be satisfied, we can integrate this component to your Joomla 2.5 site, with detailed instructions to use.
Please contact me for more details.
Regards.