Debugging Send e-mail smart service

Sned e-mail smart service hangs without showing any errors on Process model Monitor Process View -> Process Detail screen.

Also no smtp/mail related log messages available in tomcat-stdOut.log file. 

Cusom.properties setup done as per https://docs.appian.com/suite/help/19.3/Mail_Server_Setup.html

Tried using  toemailaddress/toemailrecipient - Not successful.

Any other log file i should be looking into for processuuid, custom sender emails errors? 

Is there any mail-listener log file available to check? If yes, could you suggest where/how to find this mail-listener log file location, please? - thanks.

Example Screen,