I remember that job and also building the server myself from scratch. Qmail, Squirrelmail, Dovecot and all that. It lasted about a year until we bought something as it was hell. Now days with IP reputation and spam filters - even if the server ran, you’d never get anything delivered outbound.
OP, the most I would do is an SMTP server that relays through Gmail for delivering alerts from monitoring systems. Anything else is pain.
No, set it to Dual Button Mode. If you manage to wire it backward then to check “swap inputs”.
I’m pretty sure any short press toggles on or off. Long press does a fade up/down.
First link I believe is it.
None of the second link. Those are all actual dimmers.
Seems in over the pond speak “Retractive centre off”. The idea being a hot feeds then switch. Then, depending if you press up or press down one of two momentary outputs provide power to the SW1 and SW2 ports on the Dimmer2.
Here’s another example/brand
Probably this:
https://www.bgelectrical.uk/uk/wiring-devices/grid/range/20a-20ax-3-position-modules
Google makes it surprisingly hard to search for basic hardware in other countries.
A traditional rheostat? No. You can use it with momentary switches though so that you push one way and things get brighter, push the other way they get dimmer.
Example:
That’s a router/firewall job, not a switch job.
Google “structured cabling”.