Answer by Nils for Should I put my email server in a public subnet or put in a private subnet and use load balancing / routing to route traffic from the internet?

The "general" rule is to a a three-tier-architecture.

This is typically suited for web-servers with dynamic content and a database backend.

1. First Tier: Frontend - Webserver - in your case - public IP

2. Second Tier: This is where the work gets done - Application-Server - in your case: e-Mailserver

3. Third Tier: Database - in your case propable storage groups for the mailserver.

In your case the frist tier can contain a load-balancer, a web-application-firewall or just a dedicated firewall.