I've read this and it seems to be yes, despite many media outlets Down Under (Australia also affected) reporting otherwise. Tried calling the local post office, and 800 number, but can't get a person or leave a message.
https://about.usps.com/newsroom/service-alerts/international/ Then click on the update box for November.
"New Zealand’s service disruption affects Priority Mail International® (PMI), First-Class Package International Service® (FCPIS®), Commercial ePacket (CeP), International Priority Airmail® (IPA®) packets, International Priority Airmail® (IPA®) M-Bags, International Surface Air Lift® (ISAL®) packets, International Surface Air Lift® (ISAL®) M-Bags, and Airmail M-Bags."
I don't think any of the above is a standard letter, but not really certain. And yes this is travel related, I am keeping in touch with someone I met on a tour.