A lot of Event ID 7010 – SMTP gateway

Please see error below ….
Can anyone help me with this please..I tested the server from outside of our netwrok for smtp relay and it does not realy based on my test. What action will you take next ? block all the IP’s that are coming ? any recommendation please ?

Event Type: Error
Event Source: MSExchangeTransport
Event Category: SMTP Protocol
Event ID: 7010
Date: DATE….
Time: 4:24:20 PM
User: N/A
Computer: ???????
Description:
This is an SMTP protocol log for virtual server ID 1, connection #142. The client at “XXX.XXX.XXX.XXX” sent a “rcpt” command, and the SMTP server responded with “550 5.7.1 Unable to relay for XXX@XX.net “. The full command sent was “rcpt TO: “. This will probably cause the connection to fail.