Thanks Andy for your reply. I was trying to find this explanation on internet but was not able to find so. Can you refer to me some microsoft technet article. Also
550 5.2.3 RESOLVER.RST.SendSizeLimit.Org is this error indicates that it is related to only
Organization Configuration or due to some restriction on any of receive connectors?
The exceptions for the user limits only apply to message exchanges between authenticated users. If a message is sent to or received by a recipient on the Internet, the organizational limits will be applied. For example, assume that you have an organizational
message size restriction of 10 MB, but you have configured the users in your marketing department to send and receive messages up to 50 MB. These users will be able to exchange large messages with each other, but they still wont be able to receive large messages
from Internet users because such messages will be coming from unauthenticated senders.
Note All Internet e-mail messages use the global setting for limits on sending and on receiving. The message categorizer evaluates the sender's sending limit and the recipient's receiving limit. In example 2 earlier, a
user with a user mailbox limit of 3 MB could receive messages from another user with a 3-MB sending limit. Because Internet users use the global setting, they can send only a 2-MB message.
Do individual message size limits bypass the Organization message size limits?
This is perhaps one of the most misunderstood part of message size limits, and therefore a frequently asked question: when you specify individual message size limits for a recipient, does it override other message size limits in your Exchange organization?
In a nutshell, setting higher message size limits on an Exchange recipient bypasses the maximum message sizes in the Exchange Organization configuration, but
only for internal messages, not for messages sent to or received from the Internet and other unauthenticated sources.
Remember, for a message to be delivered successfully, the message size must be within the max message size limits applicable to both the sender and the recipient. Because the identity of unauthenticated or anonymous senders and recipients cant be
established (because theyre unauthenticated!), the organizational limit applies.
and yes, that NDR implies the org limit is the issue.