In your store admin at the very bottom of the Settings > Shipping page is a place to enter in custom fulfillment vendors. Once you have added them to the list of custom fulfillment services you can then change the inventory location for their products to match. When an order is placed for any of their items they will receive an email alerting them that a product needs to be fulfilled.
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Once I create the custom order fulfillment, I went to products and went to into each item added the location to match. So if I go in and place an order for these items, the email that's associated with the email I added under custom order fulfillment will get notified immediately?