PSA the last couple of hours the default #chatmail onboarding relay nine.testrun.org was sometimes slow taking ~10 seconds to accept and relay messages. It's now back to sub-second end-to-end delivery, after tweaking some connection limit.

As is often the case, #postfix has all the needed config parameters already, and it's well documented how to tweak them, and nothing really breaks meanwhile, it only gets a bit bumpy or delayed at worst. It pays off not implementing our own server software :)