==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): Not yes installed
- Deployed with iRedMail Easy or the downloadable installer? Downloadable Installer
- Linux/BSD distribution name and version: Ubuntu 18.04 on AWS
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): MySQL
- Web server (Apache or Nginx):Nginx
- Manage mail accounts with iRedAdmin-Pro? No
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

I have a requirement for an email service that will be used by our QA department to test a web app that uses email. The requirements are that email will be sent to and received from external addresses, but there will be very few user, all internal, which will use IMAP via API calls to check for incoming mail and send/receive/reply. We don't plan on integrating this with Active Directory now, but this may be an additional requirement in the future. Most components can run on the same server, but it's been discussed that the component that actually sends and receives be in a DMZ (this is Postfix, right?). So, can Postfix be installed one server in the DMZ and the rest on a separate server on the internal network? If so, how can this be accomplished using the downloadable installer?

Thanks in advance for any help on this. I've successfully installed with everything on one server, but have not tried separating out the Postfix component.

Alternatively, if I install Postfix by itself, how can I get iRedmail to use this external Postfix server for MTA functionality?