I'm trying to install and configure Postfix/Dovecot on an EC2 instance running Amazon Linux 2. The documentation I've run across so far talks about opening ports using firewall-cmd or iptables on the EC2 instance. But are these really necessary if using AWS Security Group, wouldn't opening the inbound ports there take care of it?
I know some people want to use their own firewall on EC2 in additional to the AWS Security Group, but my question is it a requirement to use firewall-cmd/iptables so that Postfix/Dovecot can allow users to connect to pop3 their e-mail?