The direct answer
BIMI starts with the domain in the message’s visible From header. Reply-To and Return-Path have different roles and should not be used as substitutes when identifying the BIMI sending identity.
What does that look like in a real message?
From: Northstar <news@example.com>
Reply-To: support@example.net
Return-Path: bounce@mailer.example.orgIn this fictional example, start your BIMI investigation with example.com. The reply destination and envelope return address do not change which domain appears in the From header. Authentication alignment still needs to be checked.
Inspect the full source of the received message if the interface shows only a friendly sender name.
What if a platform or mailing list rewrites From?
Use the final received message as evidence and compare it with a direct copy. A rewritten From domain can change the identity being evaluated, even if the subject and company name look familiar.
Record all three fields when escalating a problem. This helps the platform owner determine whether the issue concerns branding identity, reply routing or authentication, rather than publishing a record on the reply domain and hoping it affects another sender identity.
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.