DNS basics


Domains are managed by using a worldwide system of domain registrars and databases. The Domain Name System (DNS) provides a mapping between human-readable computer hostnames and the IP addresses used by networking equipment. An understanding of DNS and domain registrar basics will help administrators manage domains in Microsoft Office 365 for enterprises.

Also, it’s helpful to have a basic understanding of DNS and the difference between domain registrars and domain hosting services. Understanding these terms can help you understand how to register and manage domains. Get a quick overview by reading the summary in Domain Name Registration and DNS Hosting Services.

What do you want to do?

  • Learn about domain names

  • Understand DNS record types and functions

Domain names

Domain names are used in URLs and email addresses associated with one or more IP addresses. Domain names are constructed in levels. For example, mail.contoso.com is a domain name with the following three levels:

  • .com is the top-level domain

  • contoso is the second-level domain

  • mail is the third-level domain


    Sometimes third-level domains are used to designate webpages that serve specific functions, such as blog.contoso.com.

For more information, see Work with domain names and DNS records in Office 365.

Understand DNS record types and functions

DNS records are used to direct traffic to and from your domain. These records associate a domain name with a specific IP address. The following table lists frequently used DNS records and their functions.

Name server record

Identifies which name servers are the authoritative name servers for a specific domain. DNS information can be cached in several name servers for a period of time, but when the cache expires, non-authoritative name servers contact the authoritative name server for updated information about a domain.

A record (address record)

Associates a domain name with an IP address.

CNAME (alias or canonical name) record

Specifies that the domain name is an alias of another canonical domain name. When a name server looks up a domain and finds a CNAME record, it replaces the first domain name with the CNAME and then looks up the new name.

MX (mail exchanger) record

Identifies the server to which email is directed. It also contains a priority field so that mail can be directed to multiple servers in a prescribed order.

SPF (sender policy framework)

An email validation system designed to help prevent email spoofing and phishing.

SRV (service record)

Specifies information about available services. SRV records are used by Lync Online and Exchange Online to coordinate the flow of information between Office 365 services. For example, the SRV records are required to see presence in Outlook Web App, and to use Lync, Skype, or other instant messaging tools with people in other companies.

TTL (time-to-live)

The amount of time that a DNS record is retained or cached by a name server or other servers before the server does another lookup on the authoritative name server. You use this to control the number of queries made to a given name server.

See Also

Add your domain to Office 365
Locate your domain services or buy a new domain
Work with domain names and DNS records in Office 365