go to transaction SCOT enter ‘dbg+’ into the transaction field and press enter -> inbound process debugging is started
send the mail (in your case by starting your report)
go to transaction sm50 and search for the waiting process in class CL_SMTP_EXT_SAPCONNECT========CP to debug it (mark it and navigate to administration > program > debugging)
debugger opens and you can set breakpoint in your class, leave the endless loop by setting cursor to line 54 and press Shift+F12, let the debugger run with F8 and you will stop next in you class
debug whatever you want ?
6)!!! After finishing you have to stop inbound process debugging in scot again by entering ‘dbg-’ and pressing enter !!! (this can also already be done when you found your process in step 3)