Ruby Nahal, Engineer By Ruby Nahal, Senior Engineer

With the rise of hosted exchange services like Office 365, it has increasingly become a challenge to preserve Outlook performance on RDS servers. Back in the day, you could only run Outlook in online mode on a remote desktop server. This was for the better because back then exchange deployments were local so we didn’t want RDS server storage filled up with unnecessary OST files.

With Outlook 2010 or later there is a way to have Outlook run in cached exchange mode on RDS servers – but there are so many cons to this. For one, there is no way to limit the mailbox contents that were cached copies in Outlook 2010, and Outlook 2010 OST files tend to grow way bigger than the actual mailbox size. (The newer versions of Outlook are different, though.)

So what is online mode v Cached Exchange Mode?

Online mode means that Outlook is opening your mailbox directly from the mailbox servers. Obviously, this works well when exchange is deployed locally because you are opening your mailbox over the local LAN.

Cached Exchange Mode, on the other hand, means a copy of your mailbox is cached locally on your computer/RDS server and you access it directly from your computer. This means less network I/O is required as only changes are synced between the exchange server and locally cached copy of your mailbox. This is possibly the best option with hosted exchange like Office 365 deployments or where your exchange server is deployed in the cloud like Amazon web services.

What is the problem with using each method on RDS server?

When your exchange is deployed locally, there is no problem with running Outlook in online mode on RDS servers. However, if Exchange is deployed in the cloud, online mode for Outlook will be painfully slow.

This can be a big hit on productivity.

With Cached Exchange Mode, unless you can put a limit on the size of the OST files (local cached copy of your mailbox), it may end up filling up the C drive on the server as that is the default location where the OST files are stored for each user. This may also hit your backups pretty hard because all of sudden you are backing up several hundred GB more (depending on the number of users and the size of their mailboxes) for something that is merely a copy of a user’s mailbox and does not need to be backed up.

What is the solution so Outlook performs optimally on the RDS server with hosted exchange?

There are certain best practices we can employ:

1. With Outlook 2016, we have an option to set the time limit on mail to keep offline. For example, we can set to keep only 3 months of mail in the cached copy and this will keep the OST file small. This can be set using group policy.

2. We can also point the OST file to another local drive on the server which is dedicated for OST files only. This drive can reside on slower cheaper storage. This can also be set using group policy.

3. Using a dedicated drive also means that we can exclude this drive from backups.

4. We can employ archiving if offered by the hosted exchange product being used. For example, Office 365 offers an archiving option for the exchange mailboxes.

Many organizations live in Outlook and so it is super critical for them to have a fair level of performance out of Exchange and with the cost of hosted services coming down, it only makes sense for most organizations to move towards hosted solutions.

About Ruby //@RubyNahal // Ruby hails from India with a flair for cooking traditional cuisine and a deep love of learning (you may find her buried in a book, non-fiction of course) and a real passion for all things tech. For her, enhancing people’s lives via well-executed technology solutions has always been more than a job, and it also makes Ruby a perfect fit for our team; she gets our mission to the core. As far as technical chops, Ruby is bar none. She holds a Master’s Degree in IT, multiple certifications and awards in Network and Security Administration, led several R & D teams and worked for five years as an Infrastructure Architect in Canada. Need we say more? Read Ruby’s story here >>