Hello Lars,
two thing to consider here:
1st: The actual number of messages per minute/hour/day the C170 can process with AV enabled. I could give some estimates about this, but experiences show that they are heavily depending on the kind of message, injection frequency, and network design. If you have any numbers you think about, feel free to post them here, and I can probably already tell you if two C170s are sufficientto handle them, or if it needs further details
2nd: While processing a lot of messages is one thing, getting them delivered is something totally different. Especial if you plan to send large amounts of messages to big hosted services such as Gmail, Yahoo, Hotmail, etc., as those only allow a certain amount of messages per timeframe (hour, day), and everything else then is queued on the appliance until the recipient hosts allows further injection. So this need special attention and often fine tuning, just using agressive delivery settings only makes these problems worse.
To make a longer story short, delivery and processing speed never has been a big problem for IronPort appliances, these boxes are simply made to deliver messages quick and efficiently. Problems are usually found either if internal mailservers causing traffic peaks by pushing out large numbers of messages in too little time, or, as already mentioned, on delivery getting throttled by the remote host.
Hope that helps,
Andreas
