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Disclaimer: my AWS networking skills are basic.

I have an EC2 Windows server instance in a private subnet. I connect via a VPN. FOR TESTING I put it in a Security Group that allows all IPV4 TCP traffic. I turned off Windows Defender Firewall. I can surf the web, so I can use port 80/443 going out. Now I want to connect to email-smtp.us-east-1.amazonaws.com on port 25.

In Powershell this times out:

test-netconnection email-smtp.us-east-1.amazonaws.com -port 25

Any suggestions where to look next?

Matthew Allen
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1 Answers1

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It is likely that you haven't requested to lift the restrictions on port 25.

AWS blocks outbound traffic on port 25 (SMTP) of all EC2 instances and Lambda functions by default.

Reference: https://repost.aws/knowledge-center/ec2-port-25-throttle

And of course after that make sure your security group allows port 25.

One note on this is that all connections to AWS SES must be TLS encrypted. I would recommend that you use port 587 or port 465 instead.

https://docs.aws.amazon.com/ses/latest/dg/security-protocols.html#security-client-to-ses-smtp

If you must use port 25, you need to figure out a way to connect to AWS SES SMTP endpoint using TLS.

I haven't tested this website but this might help

Gabrielle
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