Administrators can limit unnecessary traffic on Exchange servers without hampering the delivery of legitimate business messages. One way to accomplish this is to limit the number of recipients for mail messages.
By making a registry edit to Exchange 5.5, it's possible to limit any message to a specified number of recipients. Limiting recipients in this way prevents users from sending a message to everyone in the Global Address List.
This limit doesn't affect server-based distribution lists (DLs). You can still create DLs and assign permissions so authorized personnel can send messages to large numbers of recipients as necessary.
To implement this change, follow these steps:
Value name: Max Recipients On Submit
Data Type: REG_DWORD
Data: Enter the maximum number of recipients you wish to allow.
You don't need to stop and restart Exchange services for this change to take effect. Users will now receive an error if they try to send a message that exceeds the maximum limit of recipients, and Exchange will not send the message.
Note: Editing the registry is risky, so be sure you have a verified backup before making any changes.