Mailbox sub-folders are a very useful feature of Exchange mailboxes; they can help you file and store your different emails and share these specific folders out to other users in your organisation through permissions.
Sub-folders enable you to keep your emails organised and help to keep your mailbox clean, however there are some critical rules to remember when using subfolders to organise your mailbox.
Thank you for taking the time to read this statement, we hope together we can work to reduce item counts for mailboxes and increase the performance of your Exchange service.
Identified Issues of Large Folders
During your day to day working experience with your mailbox, you may frequently use and access many sub-folders to view and store mail; however this process can sometimes become slow waiting for outlook to load and respond to your actions.
We have observed these slow responses from Outlook on the Exchange 2007 platform and have investigated with Microsoft to identify the underlying cause of this issue. We have identified a large increase on item counts in mailboxes throughout the Exchange 2007 Platform. This has a high impact on not just your mailbox, but all mailboxes on the Exchange infrastructure as this is a hosted platform and used widely by many organisations. Organisations in the platform will notice Outlook performance issues if mailbox folders are kept near or above the Microsoft recommended item count.
Inbox and Sent Items folders <= 20,000 items
Contacts and Calendar item counts <= 5,000 items
Improving Mailbox Performance
In order to improve the performance of your mailbox and other mailboxes on the platform Cobweb recommend keeping mailbox folders tidy, and free of old unused emails.
To summarise, critical folders such as the Inbox and Sent Items are the most cached and queried by outlook and as such should be managed to reduce Items counts. Item counts for other folders such as Contacts and Calendar should always remain below 5,000 to aid performance in the rest of the mailbox.