504 Gateway Time-out: nginx
Very sorry to have missed the option on the Universal Message UI.
I enabled authentication with appropriate credentials for server. Unfortunately get dreaded "504 Gateway Time-out" error.
(A) Used PowerMessenger to independently test mail server with same credentials, using audience of 1 (myself). Works like a charm.
(B) Tried enabling debug logging option. Dialogue box unfortunately went into crazy loop when tried to select reporting option. (Had to Cntr-Alt-Delete and restart, twice).
(Thank you very much, also, for responses to other reportings).