The direct answer
The BIMI assertion is a TXT record. A CNAME can delegate the lookup to another hostname that supplies that record; it is not a substitute for a valid assertion at the destination.
What does delegation change?
The BIMI protocol draft, revision 15, describes CNAMEs for sharing configuration within a trust boundary. This is work-in-progress protocol guidance; confirm your managed service’s instructions and test the result with your target receivers.
For example, a client’s default BIMI hostname could refer to an agency-managed hostname. The receiver still needs to reach the final TXT assertion and its assets. The agency then controls a dependency that should appear in the client’s handover register.
What should I verify before using it?
Ask for the exact source hostname, target hostname and the person responsible for the target. Inspect the resolved assertion, not just whether a CNAME exists. Certificate domain coverage must still fit your deployment.
Record how the delegation will be replaced if the service ends. A deleted supplier account or missing target can interrupt an otherwise unchanged setup. Avoid adding a competing direct BIMI configuration while leaving the delegation unresolved.
Sources & further reading
Provider guidance checked on . Requirements can change; check the original guidance when implementing. Planning checklists and examples are BIMI World’s editorial suggestions.