Looking for a the most effective way to send envelope size parcels (10cm x 14cm) under 100g, globally via 3PL.

You're already saving by using a fulfillment house in each region. You could save a little more on costs by sending the product to the 3PL already picked and packed. If your product is repacked in a mail-ready package that will save some. You could take that one further and send the picked, packed and labelled product to regional mailing houses. The post office can also sometimes help with bulk mailing projects of this nature and that would eliminate your 3PL costs entirely and also ensure you're getting the lowest shipping rates.

Also, your 3PL should be providing you with information that would allow you to track this data. Why are you not getting that information? Also, why is your current operation not scaleable, have you reached the limits of your providers? Not sure I understand that part.

Here are some alternative options to consider for shipping products internationally in a more scalable way with tracking:

Use a global shipping provider like DHL, FedEx, or UPS for consolidated international shipments. They offer tracking and delivery confirmation. Rates may be higher than stamps, but they could be cost-effective at scale.

Look into freight forwarding companies that can consolidate shipments and arrange bulk international transport via air or sea. Some provide pickup from local warehouses.

Use an e-commerce fulfillment service like ShipBob, Fulfillment by Amazon, or ShipMonk. They pick up, pack, ship and handle customs and duties. More hands-off than doing it yourself.

Print shipping labels directly through your regional postal service's online portal (e.g., Canada Post, Royal Mail) for cheaper rates than couriers but with tracking.

Research group shipping discounts: some providers offer lower rates for consolidated shipments from the same sender within a time period.

Consider sea freight for large, less time-sensitive orders. Much cheaper than air but with longer transit times.

Compare parcel vs. envelope rates, as envelopes are often cheaper up to a certain weight.

Having a local fulfillment partner is very cost-effective for low volumes. As business grows, a scalable automated solution with tracking may be worth the higher per-item cost.