It is a bit overcomplicated, because I also set up SES to receive email, but I could run that instead with an ordinary Postfix server. It would be much simpler for outgoing only, I think
People don't know this, I mean no one knows this, but if you're running an EC2 instance with some allocated IPs, you can contact Amazon's customer service and ask them to unthrottle outbound mail on it. Typically they clamp down and stop connecting any SMTP deliveries off the EC2s if you do more than 10 emails/hr or something. But if you plan on keeping the IPs for awhile you can set up DKIM and SPF and all that, call Amazon and tell them you're sending and receiving legitimate business emails off that server. They may try to refer you to SES, but if you tell them you need to manage it on a private server for legitimate reasons, they have the ability to lift the block for you.
Do check your allocated IPs for blacklisting in advance, and obviously don't give them any cause for being blacklisted in the future.
https://www.pxeger.com/2020-07-02-hybrid-cloud-email-with-am...
It is a bit overcomplicated, because I also set up SES to receive email, but I could run that instead with an ordinary Postfix server. It would be much simpler for outgoing only, I think