We are having this same exact problem.  We are trying to use this module to send to our e-mail list of about 1200 subscribers.  They do not have DNN accounts in our system.  We have tried sending to 5 addresses and did not have a problem.  The e-mails were received.  However, when we tried sending to 100, no e-mail arrived.  Is there a limitation as to how many addresses you can send to?  Does the "From" e-mail address matter?  We are using a valid e-mail address in the From field.  Here are our exact settings when we are trying to send:

User Role(s):  None Selected
Email List:  We paste in our e-mails, all with semi-colons after each address
From: We are using a valid address
Subject:  Nothing out of the ordinary here
Message:  We are using an HTML message with links back to the images on our server
Advanced Settings:
No attachments
Priority: Normal
Send Method: TO: One Message Per Email Address (Personalized)
Send Action: Asynchronous

Does anyone have any ideas here?  We have tried using two of our valid e-mail servers, both of which work perfectly for everything else DNN related.  We recieve our new user registratoin e-mails all the time and both have tested out perfectly fine, so, we know that they work just fine.

Any help is greatly appreciated!

I have the same problem - I recieve emails and notifications on host and administrator acount. Also I can send newsletter to portal email box. But when I send newsletter to any other mail it never arrives. Please HELP!!!