Mail RELAY with KabelDeutschland or iCloud possible?

I've just changed my internet provider from Unitymedia to Kabel Deuschtland. With Unitymedia I could RELAY all mails from lion server throught them. With Kabel Deutschland I get only authentification problems. I've spent some days with the Technical Services without solution. Either it is not possible or they do not know how do it?

Anybody of you with the same problem? Can I use Kabel Deuschtland as RELAY mail server?

If not, is it possible to do it with iCloud?

Thanks in advance