Web client error: CNAME record conflicts with MX record
When you log on to webmail, an error indicates that the CNAME record for your domain name conflicts with its MX record. Remove or replace the CNAME record to restore email delivery.
Problem description
After you log on to webmail, an error message indicates that the CNAME record for your domain name conflicts with its MX record. This conflict blocks incoming emails. Contact your administrator to correct the configuration. The error disappears one to two hours after the DNS changes take effect.
Problem cause
According to RFC 1912, a CNAME record cannot coexist with any other DNS record type on the same host. When a CNAME record and an MX record share the same host (such as @), DNS resolvers return the cached CNAME instead of querying the MX record. As a result, the mail server address cannot be resolved and email delivery fails.
This conflict typically occurs when a domain uses a CNAME record pointing to another service — such as an Elastic Compute Service (ECS) instance or a Content Delivery Network (CDN) service — while the same host also carries an MX record for the mailbox.
Solutions
Do not configure a CNAME record and an MX record on the same host. Choose one of the following options:
Option 1: Use a different domain name or subdomain for the mailbox
Purchase the mailbox service for a separate domain name or subdomain. This keeps CNAME and MX records on different hosts entirely.
Option 2: Replace the CNAME record with an A record on the mailbox domain
Remove the CNAME record from the mailbox domain. To keep connecting to services such as ECS or CDN, add an A record that points directly to the target IP address.
Before you remove the CNAME record, verify that no active services rely on it. Removing a DNS record that other services depend on can cause resolution failures for those services.
Option 3: Move the CNAME record to a different host
Change the host for the CNAME record from @ to a different value, such as www. This removes the conflict while keeping the CNAME record in the zone.
Scope of the conflict
The conflict only applies when a CNAME record and another record type share the exact same host name. Records on different host names are not affected.
|
Scenario |
Affected? |
|
CNAME and MX on the same host (for example, |
Yes — DNS returns the CNAME and ignores the MX record |
|
CNAME on one host (for example, |
No — the records are on different hosts |
Prevention
To avoid this conflict when setting up DNS records for a mailbox domain:
Use separate host names for web services (CNAME or A records) and mail services (MX records).
Before replacing an A record with a CNAME on a host that carries MX records, verify that doing so will not affect mail routing.
Test DNS changes on a subdomain before applying them to the root domain that handles live mail traffic.