Authentication
Some ISPs do authentication of email coming through in order to avoid spamming. Then you have to provide your ISP with sufficient information.
1. Go to Mail Server->Advanced tab window
2. Enter desired host name into the Internet host name field. Usually this is the name of the computer connected to the Internet, e.g. host.isp.com.
If a user name and password are required you can only add these settings through the registry. Go to Hkey_Local_Machine/Software/kerio/winroute. Modify MailRelayAuth to '1' and MailRelayUser and MailRelayPassword to reflect the sufficient login information required by your ISP.