[foxcpp]

There is no IP whitelisting feature in maddy. I believe it is possible to do it using whatever off-the-shelf firewall you have on your system. Could you elaborate on the reasons it is not a viable way for you?

[e12e]

If whitelisting is "application level" it's easier to diagnose with an "application (protocol) level" error.

That is rather than a timeout or connection refused, an smtp 550 or 530 error with exlenation (access/relay denied; client ip not in whitelist)?