One specific postage option I noticed Japan Post had cancelled was the "surface air lift" which is a kind of middle-option between airmail (fast, expensive) and

One specific postage option I noticed Japan Post had cancelled was the "surface air lift" which is a kind of middle-option between airmail (fast, expensive) and seamail (very slow, cheap). My assumption is that this was partly because if there's less capacity on planes then you might as well use it all for expensive airmail rather than cheaper SAL. But I've not investigated whether this is really true. I think more generally trying to jury-rig cargo on a passenger plane isn't economic -- IIRC early last year some companies did a bit of it when passenger air travel was essentially zero, but they've all stopped now because (a) the cost effective way to fly cargo is to use cargo planes and (b) air passenger travel picked up a little again.