EC2 blocks&#x2F;throttles outgoing SMTP <i>by default</i>.<p>As with so many things in AWS, it&#x27;s left up to the customer to inform AWS that a) you&#x27;re running a mail server, b) what the purpose&#x2F;use case is and c) request they configure the reverse lookup associated with the elastic IP you&#x27;ve allocated.<p>Source: I&#x27;ve been running public facing SMTP servers in EC2 for years with no issues.