[Plugin: WP Autoresponder and Newsletter] broadcasting problem

Hello everyone, i hope you can help me with my problem.

I’m trying to use the WP Autoresponder by Raj Sekharan version 5.1.
Double opt-in, subscription, unsubscription, all works fine. But when I try to send an actual newsletter …. Strangely the problem is a little different each time I try it.
First the testmails worked fine but sending the actual broadcast did not. Nothing was in Queue management either before or after it was said to be send. And nothing was received.
On the second try everything was like the first, only in queue management were the right numbers. But still nothing received.
On the next try, everything worked just fine.
The when I wanted to repeat that, everythings again like try #2.

Now, letting it rest over the weekend it’s still like try #2 but the testmails don’t work either. It says it is sent, but i do not receive anything, neither testmail nor broadcast.

I really hope somebody has an idea to solve this.

By the way, WordPress version is 3.0.4
and its running on Ubuntu 10.4 lts

Thanks in advance, Annika

PS: Sorry for the double post, I had accidentally posted it in the wrong section