Why don't NDR beats come?

Question

postfix

Hey! There is such problem:
There is an exchange 2007 server, it sends mail through the server of the postfix provider.
So, on exchange, send connectors are configured with a 10 MB limit, through a smart server (relay provider) and a receive connector from the Internet and inside the organization, too, with a 10 MB limit.
If outside they try to send letters of a larger size, the sender receives nothing in response, and what is most interesting in the exchange logs, I also do not see the NDR event. If you send a big message from inside - there is NDR, there is in the logs.
I asked the provider, they have this in the postfix logs:
14:04:24.50 1 SMTP-85958([ip_exhcange_server]) [165898479] return-path rejected, got:552 5.3.4 Message size exceeds fixed maximum message size
Accordingly, it turns out that the beat comes from my server to postfix (at the beginning of my server's IP), but questions remain:
Why is there nothing in the exchange logs?
Why "return-path rejected"?