Which distribution kit to choose for the gateway + mail server?

Question

Shaping

I welcome everyone!
Please tell me the distribution kit for the server for the following tasks:
-Main gateway + firewall (DHCP, traffic shaper, reports, transparent proxy, NAT, URL filter);
-Mail server (antispam + antivirus)
Main criteria:
-free
-stable
-web-interface
Ideally, from the category of "set it up - forget it"
I'm not familiar with Linux deeply.
On FreeBSD I'm afraid I won't pull it. Users - 40 people.

Answer 1

Debian - sharp, fast, clear, stable, eats little.
CentOS - the same, if more familiar with RedHat

Answer 2

If reports are needed, then it is better that Kerio did not come up with anything in this regard. But he is paid.