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dns-record-definitions/
2017-05-30
DNS record definitions
article
2017-05-17
William Loy
2017-05-30
William Loy
Rackspace Email
rackspace-email

This article provides a brief overview of common email related DNS records.

If you need to configure your DNS for Rackspace Cloud Office Email products, see Set up DNS records for Cloud Office email.

Prerequisite

  • Applies to: Administrators and Users

For more information on prerequisite terminology, see Cloud Office support terminology.

DNS records

The following DNS record definitions also include an example of how to configure these records at your DNS hosting provider:

A record

The Address (A) record is the most basic DNS record type. It’s function is to point a domain or subdomain to an IP address

Example:

| Type | Hostname | Destination | TTL | | --- | --- | --- | --- | --- |
| A | blog.example.com | XXX.XX.XX.XXX | 3600 |

MX record

Mail Exchanger (MX) records specify a mail server responsible for accepting messages addressed to your domain. Without these records, emails addressed to your domain cannot find your mailbox. Think of it as sending a letter to an address that does not exist; the email will be returned to sender if the MX records are missing.

Example:

Type Hostname Destination Priority TTL
MX @ mx1.emailsrvr.com 10 3600
MX @ mx2.emailsrvr.com 20 3600

Note: Email hosts might ask for multiple MX record entries. These examples are actually the MX records for Rackspace Cloud Office. We require two records entries, in case the first MX server experiences a disruption. This is a redundancy to ensure you still receive your email.

CNAME record

Canonical Name (CNAME) records specify that a domain name is an alias for another domain.

Example:

Type Hostname Destination TTL
CNAME autodiscover autodiscover.emailsrvr.com 3600

Note: A common CNAME record entry is an Autodiscover Record. The example shown is the CNAME record used by our Rackspace Cloud Office users to redirect their autodiscover.example.com subdomain to our Autodiscover server (autodiscover.emailsrvr.com).

TXT record

Text (TXT) records are referenced by external sources to check for domain specific polices such as SPF, DKIM, and DMARC.

Example:

Type Hostname Destination TTL
TXT @ v=spf1 include:emailsrvr.com ~all 3600

Following are some common email-related TXT records:

  • Sender Policy Framework (SPF) records help recipient mail servers identify unauthorized use of your domain in the form of forgeries (spoofing).

    Note: If you send email from other providers on behalf of your domain, be sure to include their sending servers in the same SPF record entry. Do not create multiple SPF records.

  • DomainKeys Identified Mail (DKIM) records assign a digital signature to mail sent from your domain, marking it as authorized mail sent from your domain. If you require instruction to enable DKIM for your Rackspace Cloud Office email, see Enable DKIM in the Cloud Office Control Panel.

  • Domain Message Authentication Reporting and Compliance (DMARC) records indicate to recipient mail servers that messages sent from that domain are employing DKIM and SPF sending policies. The recipient mail server then validates the message that you sent by using your DKIM and SPF policies.

Note: SPF, DKIM, and DMARC records are important because of increased “spoofing” and “phishing” attempts. Mail recipients are adopting these methods of sender authentication to combat malicious email. This authentication not only protects those to whom you are sending mail, but it also helps identify the mail that you send as legitimate.

DNS propagation

When you add or edit one of the preceding records in your DNS zone file, it must go through a propagation period. The industry standard for DNS propagation time is 24-48 hours.

For example, if you change your domain's MX records, the change might take up to 48 hours to complete. The propagation takes so long because your domain is associated with an IP address at thousands of databases worldwide.