This thread may be old, but I just wanted to add that AT&T blocks these emails as well (sbcglobal.net accounts).

I've noticed that some work, and some won't. I still don't know what do do to make sure these are not blocked as spam. I've contacted AT&T and requested an unblock of our IP address, but I can't do this with every email company. I've noticed a lot of other threads with similar problems as this.