Dear Expert

We are using Zimbra Release 6.0.5_GA_2213.RHEL5_20100202220948 RHEL5 FOSS edition since last 4 years
but last 2 months we are facing one issue on that while sending mail in to rediff or some domain
we are getting error and mail not delivery to receipt.
Error is refused to talk to me: 553 requested action not taken:mailbox name not allow

Kindly send solution if any one having

Thanks
Manish Bajak