Planning Mailbox Quotas – Part I

When planning for storage it’s a good idea to categorise users into quota limits so you can plan your storage requirements. This calculation should be done in the High Level Design phase to allow your customer to purchase the hardware. An example of how quota limits might be categorised are shown below:-


Ø 200MB limit – Bronze limit

Ø 400MB limit – Sliver limit

Ø 600MB limit – Gold limit

Ø 2GB limit – Platinum limit


If you have mailboxes with an unlimited mailbox quota it is impossible to manage from a storage perspective as a user can effectively carry on using storage, so the unlimited users/shared mailboxes can be calculated at 2GB from a storage point of view. It’s recommended that limits are applied at something like 2GB for the following reason:-


Ø The maximum size of the .OST file (Outlook off line cache) for the unlimited mailboxes, assuming users are logging into these accounts.

Ø The .ost file performance is also another factor to consider if there are mailboxes in your organization that exceed 2 GB in size. If users of those mailboxes are running Outlook in cached mode, those users may experience degraded performance as the size of their .ost file grows above 2 GB.

Ø A limit can be set by changing the registry - If no limit is set the default is 2GB to prevent corruption and user experience as mentioned above.

Ø Specific folders can also be synchronised (if you are using Outlook 2007) therefore limiting the amount of data that be will synchronised.


When Outlook 2003 synchronises with Exchange it uses an intelligent learning algorithm that is transparent to the user. Folders used most frequently are placed in a priority order, this gives the user a better experience. The order is listed below:-

1. Utility folders (common views, views, and security settings)

2. Calendar

3. Contacts

4. Drafts

5. Inbox

6. All other folders (defined by the user)

7. Sent Items

8. Deleted Items

9. Public Folder Favorites (added by the user)


Part II will contain details on how to plan your backend storage requirements based on quota limits.


Written by Daniel Kenyon-Smith