Hi, Piyali!
As for RSWUWFML2: *Only* if you are sure that CATC produces SAP Workflow workitems, you can use RSWUWFML2. (Actually RSWUWFML2 is quite old; nowadays the recommended engine is "Extended Notifications for SAP Business Workflow" ).
As for SMTP, SCOT:
SMTP Configuration Guide - SAPconnect (BC-SRV-COM) - SAP Library