I'd imagine we are key workers.
The issue is more of what parts of our work should be considered "key". D2ds and most parcels are, realistically, far from important (in this kind of setting), but many letters and some parcels will absolutely be important.
The question is at what point it becomes necessary (if it gets to this point) to separate the important stuff out and ensure it's delivered while putting the rest on hold.
Our office had a few sick today, with a few walks still with unsorted parcels all over the bottom of the mail filled frame (that's stuffed with extra council tax letters that only arrived this morning) when I got back from my delivery (a smidge over time). As this takes hold we may see more and more go sick (or having to be off to look after kids etc), which begs the question of how long any walk can be left undelivered with less and less people on hand to go out and do it? At some point, stuff needs prioritising to go out with other stuff staying undelivered, and someone will need to take time to sift through and prep that priority stuff...
If it does go on for a few months then upper management need to have some idea of what absolutely has to go out, and who is available to sort it before it gets to the DOs, clogging them up.