Thursday 7 February 2008

How item count in Outlook folders affects performance

Where I work we see a lot of Outlook performance issues where the user's Inbox is over 10,000 items. (I think the record was about 150,000 - you can probably guess we don't use email quotas!)

Anyway this article covers some of the reasons a huge number of items in any folder will cause poor performance:

KB905803: Outlook users experience poor performance when they work with a folder that contains many items on a server that is running Exchange Server

In particular the paragraph about how recurring items are populated into the Calendar was something that had never even occurred to me before.

The one thing it doesn't touch on is how Cached Exchange Mode affects the performance. Our experience is that accessing larger mailboxes from desktop or laptop machines with slow hard disks (think not just older machines, but laptops running on battery power), Cached Exchange Mode can slow things down considerably. It's working out of the OST file (the cached copy of your mailbox on your hard disk), so if your hard disk is slow and your folders have many items, building the indexes required each time you switch views or folders will take some time.

I am generally a fan of Cached Exchange Mode (just for starters it can sheild the Exchange server from so much traffic things like Google Desktop can generate) but there are times it requires a little thought. So if your big cheese needs to keep his huge amount of mail and doesn't want his Outlook running like a dog, he's gonna need to fork out for a half-decent machine for his desk. And even then his frequently used folders should ideally stay below 5000 items.

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