SMTP email are blocking from my EC2

Hello,

Greetings for the day!

By default, Amazon EC2 throttles instances on port 25 as a spam prevention measure. Please ensure that that this restriction has been removed for your instances. Please refer: https://repost.aws/knowledge-center/ec2-port-25-throttle

Please check your account email to know if there are any blocks imposed on the instance by the AWS Trust & Safety team: https://repost.aws/knowledge-center/aws-abuse-report

You can also reach out to AWS Premium Support team via a support case and they can check the same on your behalf : https://docs.aws.amazon.com/awssupport/latest/user/case-management.html

Kindly check if you have appropriate connectivity between the EC2 instance to the destination email server. You can use commands like telnet, nc to verify the same. Please verify the Security Groups, nACL, Route Table or any OS level firewalls for any connectivity issues.

Lastly, please verify the SMTP service logs in your EC2 instance to understand more on any error codes encountered while sending the emails. I see you are using "mailhostbox". Kindly refer : https://support.mailhostbox.com/email-administrators-guide-error-codes/

Thank you