I've got Zimbra (Community Edition) running on a dabian-server with a fixed public IP. The server was told, to manage three non-commercial tld-domains. All of the config works fine, but not sending mails over port 25. The server is intended to act as a ISP-Server.

The users are not able to send mails, using the standard smtp-Port. They always get "relay access denied" after sending mail(s). Till now I didn't find a solution in the WIKI or in the forum that handles my problem (maybe I understood something wrong or I used the wrong words to search for).

I would appreciate getting some tips/links, what paramters in the config have to be changed, that allows me to send mails using this server.

If further informations are needed, pls let me know.