opening other users mailbox using rpc over http

We have 3 Exchange servers, one is a front-end server and two are backend servers.  We have a large number of remote users and no further exchange servers or VPN solution (VPN solution being developed at present).  The remote users connect to the Exchange servers using RPC over HTTPS and that works fine with no problem.  The problems start when the users try to open another users folder, from  File, Open in Outlook - or open an additional mailbox via the Tools, Email Accounts, change, more settings, Advanced "Open these additional mailboxes" option.

Whenever anyone tries this, they get a message saying the server is not available and/or Outlook should be connected.  In the status bar at the bottom of Outlook it says connected.

Can anyone suggest a way to open additional mailboxes remotely?

Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

U cant open additional mailboxes in CATCHE mode.....u need a VPN connection...
or using owa   to access ANOTHER mailbox http://urserver/exchange/username

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today

From novice to tech pro — start learning today.