First of all, make sure that you have compression enabled. To do this, open your Domino Administrator client and go to the Configuration tab. Expand the Tools menu on the right and go to Server > Setup Ports. In the dialog box, just check "Compress network data" and click OK. This should require a server restart to become active.
When I've been archviving email, I can generally see a 2:1 compression ratio. In the image below, check out 6/16 and 6/23 (apparently 6/22 is not correct). On 6/23, you can see that I transmitted 1,092,484 KBytes Uncompressed. However, only 444,062 KBytes traversed the network. This is only 40% of the data being transmitted! Not only is the good for your network admins, but it also helps you to move along to the next task faster because you're waiting less than 1/2 the time for data transmission!
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