Given a UPS presence in both countries, it would seem odd that it got handed off to USPS mid-journey. If USPS do the international leg then I would suspect Swiss Post would do the final mile.

One hopes the delivery address for UPS was Switzerland, not your shipping company's office in California...

Exactly that, why hand off to USPS?

Agree that if they were to handle the international leg - do they, generally? - then Swiss Post would finish the job.

I have seen my address as final destination on the original UPS tracking ticket...

Cost.

The package is with USPS, as a business partner of UPS Mail Innovations®

I can no longer see progress on the UPS tracking site, and the UPS tracking code is 'invalid' on the USPS tracking site.

Curiouser and curiouser. This morning I find in my inbox an email from the reshipping/store and forward company informing me that certain changes are being made to the way that USPS are working with UPS.

The UPS tracking number 'dies' at the handover to USPS and a new one is created, which I can then see on the USPS tracking site. They subsequently emailed said USPS tracking number, lo and behold the package is now in Switzerland and left Zurich presumably bound for Geneva on Sunday.

Now I'm becoming impressed. The package didn't go Zurich-Geneva, but was handed off to Swiss Post in Zurich.

The USPS tracking number has been retained and is now visible in Swiss Post.

I can see that the package cleared customs yesterday, and has been placed into the domestic system this morning.

And arrived here this morning.

USPS and Swiss Post have implemented a good interface mechanism to their respective tracking systems, I was able to see the Swiss updates on the USPS website, and the Swiss website was 'backfilled' overnight with the US tracking history.

All the major postal systems around the world have some integration. I've been able to track foreign parcels between the UK, India, Philippines, and Australia without problem (also with problems, mind - it's not perfect). UK tracking numbers start with GBR while India is IND, IIRC.