Hi Arjun,
I think you need to check follwoing:
1. t-code: swe2 you need to make sure below entry is maintained.
object type event receiver type type linkage active
ERMSSUPRT2 MAILRECEIVED WS00200001 X
2.Please run T-code: soin and then select one entry, then
->Shift+F6 (or from menu send request->display trace )to display the workflow trace
->double click the trace
->found below entry and copy the mail address after RCPT TO
log action text
INBOUND_PROC_ENTRY SMTP Envelope RCPT TO: *****@******
=> make sure you have maintained this mail address as external address in T-code: SO28
in the left field "Recipient". (not new recipient)