The Ehlo options for the client proxy target 10.10.5.123 did not match while setting up proxy for user amata/es_smtp on inbound session 08D40BBF5D3046B3. The mismatched settings might cause some messages to get rejected. Continue with proxying even though there is a mismatch. The critical non-matching options were maxSize. The non-critical non-matching options were .
You may see this error if you have multiple Exchange 2013 or 2016 servers where the max receive and transport size are mismatched across your servers on your receive connectors.