DNS record definitions

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
• MX record
• CNAME record
• TXT record

A record

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

Example:

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 system returns the email to the sender if the MX records don’t exist.

Example:

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 redundancy ensures you still receive your email.

CNAME record

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

Example:

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

External sources reference text (TXT) records to check for domain-specific policies such as SPF, DKIM, and DMARC.

Example:

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 protects those to whom you are sending mail, and it also helps identify the mail you send as legitimate.

DNS propagation

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

For example, if you change your domain 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 in thousands of databases worldwide.