Terrible.
I have to say, on regular mail delivery, USPS is pretty good. I don't remember any mail as 'not received on either end.
Toi toi toi...

I'd be certain the insurance part is better with UPS.

I once had an airplane ticket sent via UPS/overnight or so. What an ordeal.
My travel agent had to arrange for an electronic check-in, because the ticket came about 3 months later...

... with serious rubber marks on the envelope, indicating multiple forklift overruns.

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