MvV>> One of the problems with Dual Stack is that it can take a long MvV>> time to notice something is wrong when IPv6 drops out. In almost MvV>> all cases mail just keeps flowing via IPv4.
TL> I've had the opposite happen, because my IPv6 is native and my IPv4 is TL> unneled.
So your IPv4 is more vulnerable. But as the majority of active Fidonet is still IPv4 only, failing IPv4 would be noticed much sooner than failing IPv6 wouldn't it?