We are running Exchange 2007 SP3 with mostly Office 2007 clients (some people have Office 2010). We have a user that has a very large number of nested subfolders in his mailbox. The folder structure is similar to the following: \Inbox \Inbox\Client A \Inbox\Client A\1\2\3\4\ and so on... The folder structure in total reads 16,350 folders in total. The actual size of mail stored there is not the largest we've seen (it's somewhere around 26GB), but it is on the larger side. Is there a maximum amount of subfolders that Outlook can handle for a single mailbox? I've seen size recommendations for messages as well as message counts, but nothing concrete about a mailbox having to have under X amount of folders to function as desired. The user is currently using a Blackberry (on our BES) which is working fine, as I suspect the folders that are redirecting are the Inbox and not the subfolder structure. When trying to add mail to an iPhone or Android device, the mail client hangs from what I believe is the mail client trying to process the folder structure in place. If anyone has exerienced this or has any evidence to suggest what the limits are, please reply to this post. Thank you in advance

Was recently asked last month, please see below. Performance of a user with 7000+ folders (exchange/outlook 2010) http://social.technet.microsoft.com/Forums/en-IE/exchange2010/thread/31ca65d8-fe8f-4a40-8524-47c3eea46578 James Chong MCITP | EA | EMA; MCSE | M+, S+ Security+, Project+, ITIL msexchangetips.blogspot.com

The issue posted is similar was listed above -- thanks for providing the link. In combing through the responses, there's mention of no more than 10,000 items in Contacts and there is mention of items in a folder, but not specifically anything regarding subfolders. They are not experiencing issues within Outlook accessing the folders -- I'm trying to determine if there's a recommended number of subfolders that users need to stay under before performance will become an issue. Does the 10,000 apply to subfolders of the Inbox as well? If that's the case, then perhaps that's part of the problem. If this is true, then this statement would make sense: "Understand that most performance issues are not the result of large mailbox size (defined as a mailbox that is 2 GB or larger), 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 Items folder."

You are not going to get a hard number for the recommended number of subfolders. There is no white paper on how subfolders scales in depth or in width and I would surmise that it's probably irrelevant and comes down to just the items as as previously mentioned. Yes the item counts are per folder including subfolders. However you hear of "critical folders" meaning your default folders, inbox, contacts, calendars, they are more critical to be below the item counts just because they are going to be more frequently accessed. But as far as raw performance it applies to all folders. James Chong MCITP | EA | EMA; MCSE | M+, S+ Security+, Project+, ITIL msexchangetips.blogspot.com