New email bounce report?

I did an email campaign of 10,000 addresses this week, my first since the v.2008 upgrade.  After the campaign was sent, I received the standard email from NetSuite reporting Campaign Email successfully Sent with the truncated list [500] of names and email addresses.  This is normal.

At the top of the email was the regular line:

"These recipients have invalid email addresses. Please correct them:"

Usually, there will be a handful of email addresses listed with incorrect spellings, like bob@comcast.ne, etc. 

In this case however, instead of a half dozen bad emails there was a long list of 500 email addresses that were listed as invalid, even though they were visually typed correct.  Is this list of 500 invalid emails a new way that NetSuite is reporting bounces?