Port 25 has many restrictions, why not using another for a "Chatmail network"?

[Minim]

Chatmail relays used for censorship circumvention rely on looking like normal mailservers, but I guess not to active probing. Would offering an additional connection over an onion (Tor) or garlic (.i2p) site be a reasonable workaround? It could also circumvent this:

Nine.testrun.org IP flagged as suspicious - delivery blocked

My friend has lost the ability to send me messages. I’m using fastmail and it appears fastmail is using abusix. Consequently: https://app.abusix.com/lookup/results?q=37.27.110.153 When I query dns, I get a different IP address that is considered clean. I have another friend using nine.testrun.org who can still message me. It seems like the operators of nine.testrun.org need to either clear their name with abusix, or potentially investigate suspicious activity at that specific server.