If you're using an app, they can make that happen for you.
If you're manually requesting the orders, then I think you can select a box to notify the customer (I haven't done it manually in a year but it used to work like that).
This is a setting within Shopify. Check out this video that shows you how to turn on and off automatic Amazon fulfillment and email notifications!
Below are some resoures for you that include videos, FAQ's, and more information about our apps!
FAQ's - www.bytestand.com
How to use ByteStand-Import Video - https://youtu.be/yef2R2iPsTg
How to use FBA Shipping Video - https://youtu.be/D9nfPLafJDI
How to use Fresh Credit Video - https://youtu.be/WEac3HKOQ_g