

Not a problem if you are working with desktops really, but a laptop with someone who travels and may work off of the internet would have 0 access to see older emails until connected. If you select, No cache, you are pretty much at your mercy of the internet connection. You can log into your router/firewall/whatever and check your traffic so you aren't choking anything. I like to cache all the mail for my people locally as well but the initial seed can take a while especially if you have kicked this off for a bunch of users and are on a smaller pipe. Also, keep in mind most computers are building an index also if you have left the default on (which most people want so they can search mail). Yeah, it will be slow downloading 20GB of mail for sure.

If you are caching mail, it is a one time download for the inbox and then the interval defined to check for new mail. If you have "mail top keep offline" set to "all" wouldnt it have to download each message every time you click on it ? Try setting it to something like 3 months so they have immediate access to messages that are most active
