I enabled domain-mapping to an organization, but the users with that email domain were not added to the organization. Why doesn't the mapping work?
For an existing user to be automatically added to an organization when adding a domain mapping, they must have a verified email address. This occurs when an end-user completes the verification process by following the link in the verification email sent from Zendesk. Any existing users with unverified email addresses will not be automatically added via domain mapping.
If your customer is verified and was still not added, open the user's profile and make a small update to the user. For example, add a space after their name and then remove it. The organization is then added to that user. This is required when an agent or admin manually verifies the end-user's email address.
If your customer is still not added after a profile update you can temporarily remove the organization's domain or domains. Removing the domain, refreshing your page, and adding back the domain will force the mapping.
For more information, see this article: Verifying an end user's email address.