System Administration Guide: Resource Management and Network Services

Domains and Subdomains

Email addressing uses domains. A domain is a directory structure for network address naming. A domain can have one or more subdomains. The domain and subdomains of an address can be compared to the hierarchy of a file system. Just as a subdirectory is considered to be inside the directory above it, each subdomain in a mail address is considered to be inside the location to its right.

The following table shows some top-level domains.

Table 26–7 Top-Level Domains

Domain 

Description 

com

Commercial sites 

edu

Educational sites 

gov

United States government installations 

mil

United States military installations 

net

Networking organizations 

org

Other nonprofit organizations 

Domains are case insensitive. You can use uppercase, lowercase, or mixed-case letters in the domain part of an address without making any difference.

For more information about domains, refer to “Introduction to DNS (Overview)” in System Administration Guide: Naming and Directory Services (DNS, NIS, and LDAP).