Has your e-mail server ever been blacklisted? Or are you getting rejected emails? A good first step is to check MxToolBox too see if you ARE indeed blacklisted. Now, if you see one called "Backscatterer.org" you are in trouble, read this to see why.
Basically, "As it turns out Backscatterer is NOT a blacklist, It's a Sender Callout Abuser list! Nobody should be blocking mail based solely on data from a backscatter list. The only thing any mail administrator should do with this list is to use it when determining whether to flag a message as possible spam."
Good luck trying to contact them, if you want priority removal you have to pay $115.00 and it DOES NOT guarantee removal... and on thier website it says: "We don't make exceptions to our list, so it is futile and a waste of your time to contact us and ask for delisting." Really??? You can read the full thing here.
THE FIX: Get a better e-mail hosting service that checks multiple blacklist services.