DNSDNS (domain name system) services are used to lookup the IP address of a mail server for a mail domain name. The DNS services for sending messages to ISMail are somewhat different from the DNS services for sending messages from ISMail; but both must be configured properly. When sending messages to ISMail, the IP address of an ISMail domain is found using the DNS where the domain was registered (Internet DNS setup). When sending messages from ISMail, the IP addresses for other domains are found using the DNS servers configured into ISMail (ISMail DNS setup). Since these DNS services are related to network configuration (through IP addresses), network configuration settings are discussed here as well. The DNS configuration has the following parts:
Since setting up and configuring the external DNS components required to operate a mail server is a confusing process and a frequent source of error, each step should be followed carefully, and the results re-checked. See Troubleshooting for additional help. |
Internet DNS SetupISMail requires Domain Name Servers be configured in order to receive messages from other domains on the internet. Domain Name Server (MX) Records can optionally be specified as well. Domain Name Servers: use the service where a domain is Registered to setup the domain name servers. Actual working name servers must be used; not merely the name servers where a domain is 'parked'. Two name servers are required: a primary and a secondary. The name servers should be specified with textual names, and not using IP addresses (since IP addresses can change at any time). Note that setting the name servers typically requires up to 24-72 hours to take effect across the entire internet. (Optional) Domain Name Server Records: use the DNS service for the domain to setup the domain name server records (the DNS service is often the same as the service where a domain is Registered, but it may sometimes be different). Setup an MX (Mail eXchange) record, and make sure there is an A record corresponding to the MX name ('exchange' field of the MX record). Examples of Domain Name Server Records: the examples below show several different ways to setup Domain Name Server records (note the final '.' used after the domain name in these records as it is required). All of the examples assume that the ISMail Primary domain name is 'mydomain.com'. Example 1: No MX record This example shows a domain that is configured without an MX record. In this case, the A record for the domain name is used to lookup the IP address for the domain. mydomain.com. 1200 IN A 1.2.3.4 Example 2: MX record reusing existing A record This example shows an MX record that uses the existing domain name. Since an A record already exists for the domain name, no other changes are required. Many DNS services setup an MX record automatically, but some require manual setup. mydomain.com. 1200 IN A 1.2.3.4 Example 3: MX record with separate A record (ISMail using same IP as domain name) This example shows an MX record that specifies a unique name. Since no A record previously existed for the name 'mail.mydomain.com', an A record must be created in addition to the MX record, as shown. In this case, the A record has the same IP address as the domain (i.e. ISMail uses the same IP as the domain name). This configuration could be used, for example, if a web server were running on the same machine as ISMail. mydomain.com. 1200 IN A 1.2.3.4 Example 4: MX record with separate A record (ISMail using different IP than domain name) This example shows an MX record that specifies a unique name. Since no A record previously existed for the name 'mail.mydomain.com', an A record must be created in addition to the MX record, as shown. In this case, the A record has a different IP address than the domain (i.e. ISMail uses a different IP than the domain name). This configuration could be used, for example, if a web server were running on the machine with the domain name's IP address and ISMail were running on a different machine. Note that ISMail would still be configured with the domain name 'mydomain.com' (since 'mydomain.com' is the domain name with all of the email accounts). The MX record insures that any mail sent to 'mydomain.com' is actually routed to the mail server machine, which has IP address '5.6.7.8'. mydomain.com. 1200 IN A 1.2.3.4 Example 5: MX record for domain that uses 'port forwarding' (ISMail using same IP as forwarded domain name) This example shows an MX record for a domain which uses 'port forwarding' for its web server. Port forwarding is typically used when the server machine is running a web server and it is not possible to access the default web server port (port 80) from the internet. In this case, a DNS is used for 'forward' all requests for a domain to another domain on a different port. For instance, the domain 'mydomain.com' might be forwarded to 'www2.mydomain.com:81'. The web server would be configured to accept access to 'www2.mydomain.com' on port 81. The mail server, however, should still be able to use the default mail ports to send and receive email. To insure there is no interference between mail and the port forwarding function used for the web server, an MX record should be added that specifies the forwarded domain name as the mail exchanger. Note that ISMail would still be configured with the domain name 'mydomain.com' (since 'mydomain.com' is the domain name with all of the email accounts). The MX record would insure that any mail sent to 'mydomain.com' is actually routed to the mail server machine whose IP address will be found by looking up 'www2.mydomain.com'. mydomain.com. 3600 IN MX 0 www2.mydomain.com. |
ISMail DNS SetupIn contrast to the Internet DNS Setup, configuring the DNS servers to use for sending mail through ISMail is quite easy. In many cases, the default values set during product installation can be used as is. Alternately, other DNS servers (e.g. the DNS servers of your ISP) can be configured. Note: the DNS servers of your Domain Name Registrar should not be used. Many Domain Name Registrars do not support general DNS lookup for domains they do not own; therefore outbound mail can not be sent using their DNS servers. To set ISMail DNS servers to default values:
To set the ISMail DNS servers manually:
Note: do not actually use 'ns1.instantservers.com' or 'ns2.instantservers.com'. Neither is functional. If you do not know your DNS (supplied by your ISP), use the automatic DNS Setup below. |
Network ConfigurationMany server machines are separated from the internet by a router or firewall software. The documentation for the particular system used should be consulted for instructions on how to configure it for mail service. Typical changes required include enabling external access to the mail server machine for port 25 (SMTP), port 110 (POP3), and/or port 143 (IMAP4). See Firewalls for additional information, and Troubleshooting for help in setting up and testing the network configuration. |