Subscribe by Email not sending emails after new blog posts.

I have installed Subscribe by Email plugin, and it seems to be set up OK. I see my test sign-ups appear in admin fine and the front end process works well. But no emails ever go out.

As far as the settings, Autosubscribe is disabled, Excerpt is disabled, and the email subject content is basic. I'm using a multi-site install on WP 3.4 and Blogs MU theme 1.3.6.1 with the latest BuddyPress.

If anyone has a suggestion of something to try I'm all ears. Thanks!