Answer
This is stored in FNDCN_CONFIG_PARAM_TAB. Query and update the specific Mail Sender's Host parameter with something like: SELECT * FROM FNDCN_CONFIG_PARAM_TAB t WHERE t.instance_name = 'MAIL_SENDER1' AND t.area_name = 'Integration' AND t.group_name = 'ConnectorSenders' AND t.parameter_name = 'HOST' — substituting your actual mail sender's instance name if it differs. Knowing this table lets you script a host change (for example, immediately after a database refresh/replication into a lower environment) rather than relying on getting into the client to reconfigure it before any emails go out.