[_cudgel]

EC2 blocks/throttles outgoing SMTP by default.

As with so many things in AWS, it's left up to the customer to inform AWS that a) you're running a mail server, b) what the purpose/use case is and c) request they configure the reverse lookup associated with the elastic IP you've allocated.

Source: I've been running public facing SMTP servers in EC2 for years with no issues.

[brongondwana]

AWS also has an outbound SMTP service you can use:

https://aws.amazon.com/ses/faqs/

Still, unless you're running a server for a lot of people and you have tons of free time, you'll discover that it's more expensive than paying any of a bunch of people to take care of email for you.

Source: I work at FastMail

[_cudgel]

You're absolutely correct. The cost of my AWS deployment in service of my personal email, and less than 5 other people comes in at ~$5.06/mo. The time, however, is the real cost. If/when I gain significant users, Fastmail would be at the top of my list of companies to consider.