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. 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. However, if Exchange is deployed in the cloud, online mode for Outlook will be painfully slow. When your exchange is deployed locally, there is no problem with running Outlook in online mode on RDS servers. What is the problem with using each method on RDS server? 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. This means less network I/O is required as only changes are synced between the exchange server and locally cached copy of your mailbox. Obviously, this works well when exchange is deployed locally because you are opening your mailbox over the local LAN.Ĭached 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. Online mode means that Outlook is opening your mailbox directly from the mailbox servers. (The newer versions of Outlook are different, though.) So what is online mode v Cached Exchange Mode? 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.

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. 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. Back in the day, you could only run Outlook in online mode on a remote desktop server. With the rise of hosted exchange services like Office 365, it has increasingly become a challenge to preserve Outlook performance on RDS servers.

What is cached exchange mode outlook