If I want to access my Zimbra server, there is following error (with firefox):

Firefox and cannot communicate securely because they have no common encryption algorithms.
Internet Explorer tells me the Server or DNS can't be found.

If i switch the server to http (with "zmtlsctl http") I can only access the frontend.

I've restarted the server, still the same problem. What can this be?

What I did (maybe because of this it is broken): I changed the "MTA name" and the "server host name" (can't remember the correct name of this two settings). How can i reset this values with the command prompt?
Or generally said: How can I make my server work correctly?