Skip to main content

Set up Outlook on an RDS server


On an RDS - Citrix implementation, there are multiple users with multiple mailboxes and mapped shared mailboxes in use. How is it possible to set up Outlook without having connection issues but sparing disk space at the same time?

Online mode vs. Cached mode

Outlook has two modes that allows a user to interact with their mailbox: online mode and cached mode.

In online mode, Outlook gets all the data it displays directly from the server. This means that in case there's a slight network glitch, or lag, Outlook shows undesired behaviour like freezing or sent emails sitting in the Outbox for a long time.

In cached mode, Outlook creates a local copy (a .ost file) of the user's mailbox at the first start up. Afterwards, it only downloads the differences periodically and/or via push-based methods. In this scenario, a network glitch is not a problem, because the user always sees and works with the local copy, however, the local copy can take up a huge space depending on how big the user's mailbox is. If the user has mapped copies of shared mailboxes, the required space can multiply.

In case of an RDS implementation, this required space is again multiplied by the number of users on the RDS server. It can even reach hundreds of gigabytes of occupied disk space.


The solution to this catch 22 is configuring something in between: configure the users' mailboxes with cached mode BUT configure it to download ONLY cca. 2 weeks (at most 1 month) of data. And not the whole mailbox.


Do everything the way you'd do when setting up an Outlook profile, but at the end tick in "Modify account settings"


Tick in "Cached Exchange mode" and define the 2 weeks.


User experience

The user will see only the emails that has been in their mailbox for the last two weeks. 


If they click on "Click here to show further information on the server" the emails that are older than two weeks appear - but they are not downloaded. They are shown as if Outlook was in online mode.


If the user searches for an email that is older than two weeks, they will get a prompt to search on the server side. 


Clicking on the button, the older emails show up.


Mapped mailboxes

Mapped mailboxes put an even bigger space requirement against the server. Consider the following: if a shared mailbox is mapped for 10 users - that shared mailbox will be downloaded 10 times for each of the users who has access to it. To avoid this but to have a simple and easy access to these folders, instead of mapping shared mailboxes, we offer Mailstore as a solution.


Mailstore is an email archival solution which offers an Outlook add-in. Using the add-in, the emails of shared mailboxes can be browsed and viewed without having to download them to the RDS server.