i'll be migrating the postfix install to use this net namespace
so that IPv4-only mailservers have a port25-unblocked IP to contact
(HurricaneElectric gives a port-25 IPv6 /64 block for free, but
Zoho won't send mail to it. gmail does. didn't test other providers)
not tested:
- sending to root
- receiving from an external domain
- sending to an external domain (definitely won't work, since the DNS keys aren't correct anymore)