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DNS Records used by Exchange server and the function of each



Article Summary: This article provides information on DNS records used by Exchange server and the function of each.


Table of Contents:

1.Required DNS Records
2.Optional DNS Records
3.Function of each DNS Record type
4.How to verify DNS Records


1. Required DNS Records

There are 3 DNS record types that are required for Exchange. Without them, some outgoing mail will be delayed or rejected.

  • A record that points to server sending and receiving mail
  • One or more MX records
  • PTR or Reverse Lookup record

2. Optional DNS Records

There are several optional DNS records. While optional, most are recommended as they will make administration simpler.

  • SPF (Sender Policy Framework) record
  • Autodiscover A record
  • SRV record for Autodiscover
  • Separate A records for different Exchange services

NOTE: It is not advised to create both an Autodiscover A record AND a SRV record for Autodiscover. Typically one or the other would be utilized.


3. Function of each DNS Record type

Each DNS record type has a function. Below is an explanation for each and how it applies to Exchange server.

  • A record: This type of record simply resolves a name to an IP address. It is sometimes referred to as a host record. Exchange utilizes A records for both mail flow and service entry points. For instance, a typical A record most organizations use is mail. The A record is then added to the domain name to get the full address. Using the mail example, a company with the domain name smithbakery.com would have an address of mail.smithbakery.com. Optionally separate A records can be created for services. This is typically done for very large (10,000+ users) Exchange organizations. For instance, owa, outlook, and oab are commonly used for OWA (Outlook Web Access), Outlook Anywhere, and OAB (Offline Address Book) respectively.
  • MX record: This record is responsible for pointing other mail servers to the server(s) that will accept mail for a given domain name. There are 2 parameters required for this record type; priority and name. The priority is utilized when more than one MX record exists for a domain name. For instance, there are 2 MX records for dell.com; 10 smtp.ins.dell.com, and 20 smtp2.ins.dell.com. The first record, 10 smtp.ins.dell.com, has a higher priority and would be attempted first. If the first server did not respond or refused the connection, the second server, 20 smtp2.ins.dell.com, would be attempted. This process would repeat for all MX records until a connection can be made and the message handed off.
  • PTR record: This type of record simply resolves an IP address to a name. It is sometimes referred to as a reverse lookup or pointer record. Using the smithbakery.com example from above, this record should be the domain name, smithbakery.com, or match one of the MX records. If this record is not present or is incorrect, then it is very likely that some emails will be rejected. This is due to some administrators using the PTR record as a spam control device.
  • Autodiscover A record: This A record is responsible for auto-configuring clients, such as Outlook, Entourage, and mobile phones, and pointing them to Exchange services. This is an optional record, but is strongly recommended as it streamlines the client setup process. This record is simply autodiscover. Using the smithbakery.com example from above, the full domain name would be autodiscover.smithbakery.com.
  • SPF record: This record type is used to inform other mail servers which hosts are authorized to send mail for a domain. This is an optional record. This record is commonly used for spam control. If a record exists and is configured correctly it can assist a message in getting through spam controls. For information on creating an SPF record see the following knowledge base article: How to create a SPF DNS record.
  • SRV record for Autodiscover: A SRV record is a text record that points to a specific service in a domain. In the case of Autodiscover, the SRV record points clients to the address of the Exchange server. This record is typically used in place of the Autodiscover A record, so that a single name certificate can be utilized for Exchange. For information on creating an SRV record see the following knowledge base article: How to create a SRV record for Exchange server.


4. How to verify DNS records

To verify that DNS records for Exchange have been created and/or are correct, go to the MX Toolbox.

  • A records: Use the search box labeled "a" and type in the full domain name.
  • MX records: Use the search box labeled "mx" and type in the domain name only. For instance, if I wanted to retrieve all MX records for dell.com, I would type in dell.com.
  • PTR records: Use the search box labeled "ptr" and type in the internet IP address.
  • SPF records: Since SPF records are txt records, either the "spf" or the "txt" search box can be used. In either case, type in the domain name. For instance, if I wanted to retrieve all SPF records for dell.com, I would type in dell.com.
  • SRV records: Since SRV records are txt records, use the "txt" search box, and type in the domain name. For instance, if I wanted to retrieve all SRV records for dell.com, I would type in dell.com.

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Quick Tips content is self-published by the Dell Support Professionals who resolve issues daily. In order to achieve a speedy publication, Quick Tips may represent only partial solutions or work-arounds that are still in development or pending further proof of successfully resolving an issue. As such Quick Tips have not been reviewed, validated or approved by Dell and should be used with appropriate caution. Dell shall not be liable for any loss, including but not limited to loss of data, loss of profit or loss of revenue, which customers may incur by following any procedure or advice set out in the Quick Tips.

ID do artigo: SLN266073

Data da última modificação: 09/26/2014 11:49 AM


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