Kerio mailserver webmail (over the internet)

I installed kerio mailserver a few weeks ago and had everything up and running. Now i'm trying to configure the webmail part. It works on the LAN but I want to be able to check my mail over the internet. I already forwarded all necessary ports but how can I view it now? The fact that it is Kerio mailserver isn't really important I think. I tried it with sharepoint services as well but I can't get it to work. (I must say I don't know very much about all this).