Does the customer get an email for every supplier's shipment?

Yes. Shopify sends a shipping confirmation for each fulfillment, as for any partly shipped order. You can switch off the confirmation for supplier shipments in SplitFlow's supplier settings.

What if a supplier mistypes the tracking number?

Open the order in Shopify and edit the tracking on that fulfillment, as you would for any shipment.

Which carriers can suppliers choose?

The common ones in Europe and North America, such as DHL, DPD, GLS, Hermes, UPS, FedEx, USPS, Royal Mail, PostNL and Correos. For any other carrier the supplier types its name and can add a tracking link.

How to get tracking numbers from your suppliers into Shopify

When a supplier ships for you, the customer's shipping confirmation should go out with the supplier's tracking number. Usually the number arrives by email, and someone copies it into Shopify — late, and one order at a time.

Short answer: Shopify sends the customer a shipping confirmation when items are marked as fulfilled with a tracking number. You can add the tracking by hand on the order page. If your supplier is connected through Shopify Collective, it comes back automatically. Otherwise, give each supplier a private link where it enters the tracking itself and its items are marked as shipped for you.

Option 1: add the tracking by hand

In your Shopify admin, go to Orders and open the order.
In the Unfulfilled section, click Fulfill items.
Select the items the supplier shipped and enter the tracking number. Shopify usually recognises the carrier from the number.
Leave Send a notification to the customer checked if the customer should get the shipping confirmation, then click Fulfill items.

Fine for a few orders a week. With several suppliers and many orders, the copying is where delays and typos creep in.

Option 2: Shopify Collective, if your supplier is on Shopify

When your supplier sells on Shopify and you import its products through Shopify Collective, orders go to the supplier's admin and the tracking number syncs back to your store, which then sends your usual shipping confirmation.

Option 3: let suppliers add the tracking themselves

Install SplitFlow from the Shopify App Store and open Suppliers.
Add each supplier with its email address and which items it ships, usually Vendor equals the supplier's name.

SplitFlow emails each supplier its items from every new order, with a private link. In the portal the supplier enters the tracking number, picks the carrier from the list — DHL, DPD, GLS, UPS, FedEx, USPS, Royal Mail, PostNL, Correos and more — or types another carrier's name, and clicks Mark as shipped. SplitFlow marks exactly that supplier's items as fulfilled in Shopify with the tracking, and Shopify sends the customer its shipping confirmation.

Good to know

One order with several suppliers: each supplier marks only its own items. The order shows as partially fulfilled until everything has shipped, and the customer gets a shipping confirmation for each shipment.
Items you ship yourself are never touched.
SplitFlow's Suppliers page lists every order sent to a supplier, with its status and tracking.

Questions

Does the customer get an email for every supplier's shipment?: Yes. Shopify sends a shipping confirmation for each fulfillment, as for any partly shipped order. You can switch off the confirmation for supplier shipments in SplitFlow's supplier settings.
What if a supplier mistypes the tracking number?: Open the order in Shopify and edit the tracking on that fulfillment, as you would for any shipment.
Which carriers can suppliers choose?: The common ones in Europe and North America, such as DHL, DPD, GLS, Hermes, UPS, FedEx, USPS, Royal Mail, PostNL and Correos. For any other carrier the supplier types its name and can add a tracking link.