On the Fax on Demand Mailbox page for the mailbox, make the appropriate changes:
In the Last Name box, type the name of the Fax Overflow Mailbox. The name can be a maximum of 16 characters.
In the Fax Retries box, type the number of times to try to deliver queued faxes. Undelivered faxes are sent to the General Delivery Mailbox. The number can be between 1 and 99. The default is 99.
In the Fax Interval box, type the number of minutes to wait between delivery attempts. Set this interval as short as possible to send queued faxes to the fax machine before it becomes busy with more incoming faxes. The number can be between 1 and 60. The default is 1.
After you make your changes, click the Submit button.