Event 201,290 in exchange 5.5

We have Exchange 5.5 server with Sp4 installed.
This also works as the bridgehead server in the site and also has IMS connector. Oflate we are seeing more 201 & 290 event id’s in eventviewer.
Source : MsExchangeMTA
Category : X.400
For 201 it says loop has detected and for 290 it says non delivery.checked msdn for info but no exact info for our errors.

what could be the reason for this.