Establishing a Mail server: Overview (2)

server | mail server mail system to be able to identify a variety of different formats of the address (the recipient and sender of the letter). The most common formats are the UUCP format and the domain name format. The address of the UUCP format (with an exclamation mark) clearly lists the path from the addressee to the sender, such as the address "bill!bird!keyanbu.com!paul" stating that the new drug passed through bill, after Bird, Then after keyanbu.com, finally arrived at the addressee Paul's hands. The Domain name format (for example, zzy@keyanbu.com) identifies the path from the addressee to the sender through a dedicated address resolution system. Although the two formats are the most common, other address systems exist.

1.5 The routing Choice routing of the Mail system is an important function that the MTA program provides to the user, and this function changes with the change of address format, because the address of the UUCP format has already determined the route, and the address of the domain name format needs to choose route. For a connection based on a TCP protocol, the MTA program passes the message to the destination host based on the IP address, allowing the IP protocol to select the route.

To simplify the mail delivery process, you can use the local area network to publish an MX (mail eXchange) path. This MX record has a DNS explanation. It directs the message to select routes. This scenario is for a network that is used for large-scale networks or where only one interface is connected to the Internet. This MX record can be a host that is not always connected to the Internet to receive messages received by the mail server. Here is an MX record:

Abc.zgjsyh.com in MX 3 mallserver.zgjsyh.com

This tells the DNS system that any messages sent to abc.zgjsyh.com should be passed to the system mailserver.zgjsyh.com. The "in" record is the resource record type, and "MX" indicates that the record is an MX record. The number "3" in the example is the priority sequence number, which is used to determine the priority of the server. A network can have several mail servers, each of which is given a priority sequence number. The software that transmits the mail first chooses to transmit to the server with smaller serial number, if the small serial number server does not have corresponding, in the server that sends the serial number to be bigger.

UUCP the way a network handles mail is completely different from a TCP network. In the early days of UUCP network development, the entire path was clear because every hop (hop) from the source address to the destination site had to be determined. With the expansion of the network scale, it is almost impossible to determine the address, so the mapping system emerges. The UUCP mapping system maintains a table containing all the official UUCP site names and the sites that are adjacent to them. The mapping system receives requests from the MTA program based on UUCP to search the path to the destination for the MTA program. These mappings are called Usenet mappings, and they periodically publish information about the UUCP site to the Internet.