Can't Get Email From Suddenlink.net Server

I have Suddenlink for my service. I can get on the web and get my mail through apple mail (Icloud, gmail, yahoo) but not Suddenlink email. I can get my Suddenlink email on my iphone and ipad. When I sign in for email with Suddenlink on my computers, I get a message that says that it can't authenticate my user name. We called Suddenlink and they said it was a apple problem not on their end. Please help.