I have found other posts where people are having the same problem. Rather than explain it, just view this post - http://forums.verizon.com/t5/Verizon-net-Email/Verizon-blocking-my-IP/td-p/621425. My situation is very much the same.
I run a server with client websites, many of which use web mail. These are mostly non profits, they don't do spam, nor do I.
In the last week, Verizon has blocked all incoming email from my IP address which affects a number of organizations. There was an issue with one spam service (Rats) which was fixed within an hour. It's now been a week and it's still not fixed. Today one of my clients tried to send out a newsletter and got 49 bounce backs.
Today I went to the trouble of installing a SSL Certificate and even paid extra to get a new IP address figuring that the problems would go away. But it's the same thing all over again. I checked the IP address before installing it and it was clean as a whistle.
It's like the whole office is on vacation. What gives?