Where can I find information on how to configure the Email connectivity in KM?
The steps on how to configure Email connectivity in KM are described in SAP Help:
http://help.sap.com/saphelp_nw04/helpdata/en/7c/6a469702474146a8ef2f97fe880b2f/frameset.htm
I've done the Email connectivity configuration (and "sent to" works fine) but I still don't get any notification mails. Where can I find a good explanation for the use of the different E-Mail channels in KM?
Check out Dirk Lehmanns detailed explanation in this thread: https://forums.sdn.sap.com/thread.jspa?threadID=56421
I still have some problems with the EMail connectivity. What can I do to check if the problem relies on the portal side or if there is something with the connection to the SMTP server?
I would recommend going through this thread and all the further threads that start from there. In particular the threads mentioned by Dirk Lehmann are extreme valuable. (If those links do not work, just copy the threadID and put it in another thread-URL).
If you have gone though all the threads and you still have no solution, I would suggest opening an OSS ticket.