Newsletter not sending preview

Hi There,

I would like to test the new eNewsletter plugin but I don't get it running. Whenever I want to send a preview I get the following error messages, depending on settings:

When I use SMTP
Mailer Error: The following From address failed: : Called Mail() without being connected

When I use PHP
Mailer Error: Could not instantiate mail function.

Any idea what I do wrong?

Thanks, Tee.