[eluser]Matt Stein[/eluser]
I'm having the exact same problem. To test, I generated a list of 100+ bogus email addresses at my own domain, and inserted a real address (of my own) at various points within the list.
We discovered this problem by sending out a 3000+ email blast, so I'm hoping my bogus address trick will be sufficient for testing.
I originally followed <a href="http://ellislab.com/forums/viewthread/69935/" target="_blank">this thread</a>, thinking the HTML was the problem. I corrected my emails to make them entire pages including HTML, HEAD, and BODY tags.