550-x.x.x.x locally blacklisted for bruteforce auth (username+password) 550

The same email can be sent on a machine other than AWS. What is the situation? thank you!

SERVER -> CLIENT: 550-x.x.x.x locally blacklisted for bruteforce auth (username+password)
550 cracking attempt
CLIENT -> SERVER: EHLO ip-x-x-x-x
SERVER -> CLIENT:
SMTP ERROR: EHLO command failed:
SMTP NOTICE: EOF caught while checking if connected
SMTP connect() failed.

Feedback from AWS:
We have reviewed the IP address x.x.x.x and we can confirm that the email sending limit for port 25 have been lifted for the Singapore region.

How can i deal with it? Thanks.