"Big pipe". Because MAPI over the web is a hog.
To me, it sounds like you'd like to set up Outlook to "download" mail from an Exchange server, i.e POP3.
If so, this is very easy to implement.
Exchange Administrator ->
ORG -> SITE -> Configuration -> Servers -> ServerName -> Protocols -> POP3
If your server is behind a firewall, ensure that the IP address of the mail server has ports 110 and 25 open (sounds like 80 is allready open for OWA).
Of course, you know the story about the negatives of POP3?
Hope that helps
Sky "Nuclear war can ruin your whole compile."
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