scaling of DNS & mail servers

[Matthew Thompson]

> Just a quick question. I have a series of small qmail servers 
> (6 of 'em so far) and our organzation is scaling mail 
> linearly for now.  (I don't see us getting above 6 any time 
> soon though...)

> I'm planning on implementing this and locking the box down 
> properly (no queries from anyone but itself), but I wanted to 
> hear what others had to think about this type of scaling.  
> Are there any other ideas on how to scale mail and dns properly?

What sort of throughput do these servers get?