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SMTP port 25 is blocked by default. You have to apply for port 25 to be unblocked for your account. Alternatively you could use a 3rs party such as Sendgrid.
AWS email offering includes SES but again it’s in sandbox mode until you apply to move it to production.
You are leaving out a lot of details - such as what this website is built on - and where it is running. However, I will make some assumption - since you mention that it cannot send e-mail.
If you are running this website on an EC2 instance (or you are using a Lambda function to send SMTP email directly) within AWS - then you will not be able to send SMTP email to external mail servers on TCP port 25.
You can read about this restriction here: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-resource-limits.html#port-25-throttle
To remove this restriction - you can follow the process described here: https://repost.aws/knowledge-center/ec2-port-25-throttle, or you can use The Amazon Simple Email Service (SES) to relay the e-mail for you.
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Hi Gary, Thank you for your response. what would cause this to be blocked? We were using this website and then suddenly it stopped working.
Not knowing your full setup it would be hard to tell if something else in the process is now failing like a lambda function etc.