The most common places that you configure message sizes are:
- User. The maximum send and receive sizes that you configure for a user override the settings configured for levels. The allows you to create exceptions for specific users that are larger or smaller. Configure in the Mail Flow Settings tab of the user.
- Organization. This controls the maximum send and receive message sizes used by all Hub Transport servers in the organization. The default size is 10 MB. Configure in Organization Configuration > Hub Transport > Global Settings > Transport Settings > General tab.
- Receive connector. Each Hub Transport server has receive connectors with a default maximum receive message size. This should match the setting for the organization unless you want a specific connector to be more restrictive than the organization. Modify on the General tab of the receive connector.
- Send connector. Send connectors are used primarily for message delivery to external systems, including the Internet. This setting should match the setting for the organization unless you want a specific connector to be more restrictive than the organization. Modify on the General tab of the send connector.
For more detailed information about message size limits in Exchange 2010 see Understanding Message Size Limits in the Exchange 2010 SP1 help at http://technet.microsoft.com/en-us/library/bb124345.aspx.