Ben Forchhammer has just released a new plugin called Mail Debug.
This plugin could be of great assistance in finding out why emails are not being sent when using Subscribe2. The documentation states:
This plugin when activated automatically redirects all email sent through wp_mail/phpmailer to the user currently logged in.
The redirected email contains information about where the original email would have been sent to.
Use this plugin if you want to test email-sending features without actually sending emails our to anyone but yourself. I wrote this plugin to ease debugging with subscribe2.
So, if you are having problems with Subscribe2 then give this plugin a try.