Hi Prakash,
MSGFN is the "Message Function". It's a code that defines the action to be performed with (or by) the IDoc itself. Supported codes are:
003 Delete: Message contains objects to be deleted
004 Change: Message contains changes
005 Replace: This message replaces previous messages
009 Original: First message for process
023 Wait/Adjust: Data should not be imported
018 Resend
Thanks & regards
Saifur Rahaman