AWS - Covert AWS-supplied .pem files to the XML format

To use the RSA keys provided by AWS Account/Security in the .NET framework, you must convert the AWS-supplied .pem files to the XML format that the .NET framework uses. You can use below link to convert. 

 https://superdry.apphb.com/tools/online-rsa-key-converter

AWS - Message delivery to the remote domain failed for the following reason: The remote server did not respond to a connection attempt.

Error - Message delivery to the remote domain 'gmail.com' failed for the following reason: The remote server did not respond to a connection attempt.

 Amazon Web Services’ EC2 instances are throttled on port 25 by default as a spam prevention measure. This can cause connection issues when attempting to use SMTP to relay emails through Postmark in your EC2 instance. There are a couple ways to resolve this issue so that you do not receive connection errors when using Postmark in your EC2 instance. 

How do I remove the throttle on port 25 from my EC2 instance?

Issue

I'm having trouble sending email over port 25 of my Amazon EC2 instance, or I'm getting frequent timeout errors. How do I remove the port 25 throttle on my EC2 instance?

You can request Amazon Web Services to remove the throttling on port 25 using theRequest to Remove Email Sending Limitations form. Note: you must sign in with your root account credentials. Amazon Web Services will request that you provide a use case description with your request to remove the throttle. Once your request is approved, they will alert you via email that the block has been removed.

please check the link - https://aws.amazon.com/premiumsupport/knowledge-center/ec2-port-25-throttle/