Yes, Transact supports multiple custom domains within the same Transact organization. If you support multiple brands and domains, you can manage and send all of your Transact messages from one Transact organization, regardless of the number of custom domains.
Provision the custom domains in Organization Settings > Domain Settings.
To send Transact messages from multiple custom domains in the same organization, you must assign the correct custom domain to the appropriate Transact database. You can set this value in Database Settings.
Transact sends the message from the custom domain that is specified in the database that is assigned to the Transactional Automated Message Group (also called Transact Campaign). If a custom domain is not specified in the database, then Transact sends the message from the organization default domain, which is specified in Domain settings.