A flexible gateway would be a great add on, I also like a private DNS server while developing. If you offered a Postfix forwarder and static, clean IP addresses

A flexible gateway would be a great add on, I also like a private DNS server while developing. If you offered a Postfix forwarder and static, clean IP addresses, you could attract home users who wish to host their own email but are behind dynamic residential connections (like me, I use a digital ocean droplet currently for that purpose).