Common sense tells us that large mailboxes will slow the performance of Exchange Server. But are you aware that item count is the real nemesis of Exchange performance? We recently found this TechNet article, which does an excellent job of explaining the difference between mailbox size and item count — and explains the corresponding impact on Exchange Server performance.
Here’s a brief excerpt from the article that makes a key point about item count:
Understand that most performance issues are not the result of large mailbox size (defined as a mailbox that is larger than 2GB), but instead the number of items in the folder or folders that are being accessed on the server. Having many items in a folder adversely affects performance because operations in those folders will take longer. In particular, performance is largely influenced by the number of items in the critical path folders: Calendar, Contacts, Inbox, and Sent Item folder.
We urge everyone who is responsible for Exchange Server to carefully read and understand this article. We live in a time where rapid mailbox growth is the norm, and it is critical for the successful management of Exchange that we manage email storage growth with a complete understanding of how Exchange works.