deblacklist my email domain

Hi, Our email domain is blacklisted. On only 1 list, but its hurting us badly. We NEVER send newsletters so how we became listed is a big question for us. Can somebody help unlist us? And also, when we had google apps we had an option to add a SPF list or something that was related to this, maybe its good to use that. Again, i dont want a trick or scam or whatever, we are really sincere and i have no idea how we got blacklisted. Its important it gets fixed though. Thanks Robert