>So, when qmail hits a peak (perhaps somewhat sustained - remember its a
>relay, no spam would hit it) concurrency of 200, and the average msg
>size is 15K, we are looking at coresponding peak bandwidth usage of
>1.0Mb/s. Sound reasonable?
Unfortunately no. There is no real correspondence between your message
profile and your peak bandwidth.
Consider the simple situation of a, say, a single 1Mbyte email. If the
sending system can send at, say, 2Mbits per second and the receiving end can
accept at 2Mbits per second, then the transmission of that message will go
out at T1 speeds. In other words a single message can cause a 100%
utilization on your link, albeit for less than 8 seconds in this case.
Your peak bandwidth utilization will be a function of the aggregate transmit
demands and the aggregate receive capabilities. It may be that a single
1Mbyte email to a fast location saturates your link but 200 concurrent
emails to slow locations will not.
Now if you mean average, that's another story.
Mark.
