We have an offsite terminal server that has always used Outlook Classic in Online Mode, so switching to Cached Mode is currently not practical. For roughly the past two weeks, the delay between new emails appearing in Outlook has become extremely long. Outlook on the web refreshes quickly, and the data center connection, bandwidth, and server resources all appear healthy. The main problem affects several very large shared mailboxes rather than users' primary mailboxes, with around 20 people connected concurrently. I'm looking for ways to identify what is causing the slowdown and determine whether the mailbox size, shared-mailbox configuration, or Outlook client is responsible.
3 Answers
How large are these shared mailboxes, exactly? Mailboxes approaching their service or storage limits can become extremely sluggish in the desktop client, whether Cached Mode is enabled or not. Checking mailbox size, folder sizes, item counts, and quota status would be a good first step.
Large shared mailboxes tend to perform poorly in Outlook Online Mode on a terminal server. A practical workaround is to keep users’ primary mailboxes in Classic Outlook but have them open the oversized shared mailboxes in Outlook on the web instead. That avoids making every Outlook session repeatedly query the largest folders and mailboxes.
Cached Mode with profile-container technology could be worth revisiting if storage is the only reason it was ruled out. It can reduce repeated server queries in a multi-user terminal-server environment, although the storage requirements for these large shared mailboxes still need to be planned carefully.
The main concern with Cached Mode is the storage footprint, especially because the shared mailboxes are the ones that have grown so large.