efa-project.org

I have read this:
https://wiki.efa-project.org/doku.php?id=setup_guide

Is minimum requirements 8gb of ram?

Yup, for a small install you could get by with just 4gb but 8gb should be your starting point if you use it for a number of domains.

I've been live now with 2GB RAM on Hyper-V and 2 vcpu's.
Webmin is showing a stable 61% usage on RAM.
Processing up to 500 mails an hour is very small, but let that be an indication of my very small setup.

If it would be at the office, ofcourse it will be 8GB/4cpu