Outlook clients get "Contacting the server for information"

Hi,

I've recently setup a new production Exchange 2010 Enterprise Edition server running on Windows 2008 R2 Enterprise.  Everything is working fine except for user's are getting a pop up in Outlook 2010 that says "contacting the server for information" when fowarding messages with imbedded html.  Outlook 2007 user's don't get the pop-up, but it still takes a long time for the message to send.  After they click the send button, it just sits on thier screen for about 20 seconds.  All other email messages are fine.  The messages are small, even a 26kb message will do this.  Has anyone seen this before, or have any ideas about what needs to be changed for the messages to be sent out at an acceptable time.  All users are configured for cached mode in Outlook and this happens for user's on the same LAN as the server and for user's on a different LAN.  At this point, we only have 10 or so user's on the server, but are getting ready to migrate several hundred over. 

Thanks,
JScott2