Use the WebAdmin Interface to configure the Resolver settings. Open the Network pages in the Settings realm, and follow the DNS Resolver link.
Log Level: Use this setting to specify what kind of information the Domain Name Resolver should put in the Server Log. Usually you should use the Major or Problems levels. In the later case you will see the information about all failed DNS lookups. If you use the RBL services, you may see a lot of failed lookups in the Log. When you experience problems with the Domain Name Resolver, you may want to set the Log Level setting to Low-Level or All Info: in this case protocol-level or link-level details will be recorded in the System Log as well. The Resolver records in the System Log are marked with the DNR tag.
Concurrent Requests: This setting limits the number of concurrent requests the Resolver can send to Domain Name Servers. On a heavily-loaded Mail or Signal relay processing many thousand requests per second, this parameter should be selected after some testing: older DNS servers may crash if requested to process too many concurrent requests.
DNS Addresses: This setting specifies how the CommuniGate Pro Server selects the DNS servers to use. If the OS-specified option is selected, the Server reads the DNS server addresses from the Server host OS. To force the server to re-read those addresses, click the Refresh button on the General page in the Settings section. If the Custom option is selected, the CommuniGate Pro Server will use the DNS servers addresses listed in the text field next to this pop-up menu. If no DNS server address is specified, the CommuniGate Pro Server uses the 127.0.0.1 address, trying to connect to a DNS server that can be running on the same computer as the CommuniGate Pro Server.
Balance Server Load: If this option is disabled, then the initial request is always sent to the first DNS server in the list, and if there is no response from that server, the request is resent to the second DNS server, etc. If this option is enabled, then initial requests are sent to different DNS servers: the first initial request is sent to the first DNS server (and if it fails - the request is resent to the second DNS server), the second initial request is sent to the second DNS server (and if it fails - the request is resent to the third DNS server), etc. Enable this option if your Server performs a lot of DNR operations and it can use several equally effective DNS servers.
Use Supplementary Responses: If this option is enabled, then "supplementary" records in MX and SRV requests are processed. These records contain the IP addresses (A and AAAA records) for the domain names listed in an MX or SRV response, so no additional DNR request is needed to retrieve these IP addresses.
Initial Time-out: The Domain Name System uses the connectionless UDP protocol by default, and if there any network trouble, a UDP request or response can be lost (while the TCP protocol automatically resends lost packets). The Domain Name Resolver waits for a response from a DNS server for the period of time specified with this option. If a response is not received, the Resolver resends th