I have a Postfix instance on an EC2 server which will need to accept mail from the outside world (e.g. port 25 will be mapped to it from a virtual IP.)
I also want to use this server to send mail from my other EC2 machines. As EC2 doesn't map to the concept of a subnet which can be granted relay access, I'm thinking about running Postfix on a second port, and limiting access to that port by security group.
Ultimately I want port 25 to run like normal, and have port 26 accept mail for anyone who is able to connect to it.
Can this be done?