In the Israeli company I work for, it has become common to use the verb 'stuff' for letters in an envelope, in company business writing. This usage sounds highly irregular to me (unless your trying to cram a stack of A4s into a small envelope), and I'm wondering whether it's an Israeli invention...

In case I'm correct in this assumption, does anyone know of an appropriate verb describing the action of simply putting a letter into an envelope?

Thank you!

The expression "stuffing envelopes" is quite common here in the US. In fact, it's even a business opportunity. You'll often see ads reading: "Make big money by stuffing envelopes at home!" (I never tried it). Now that you've pointed it out, though, I agree, it does sound rather strange.

I have a friend whose printing works used to have a mechanical stuffer - a device that folded letters, and inserted them into envelopes. This machine was ancient last time I saw it, don't know if it is still in use!

The expression seems to be in fairly common usage. M-W gives the following definitions:

Stuff vt (1a) : to fill by packing things in

Stuffer n (2): an enclosure (as a leaflet) inserted in an envelope in addition to a bill, statement, or notice.

It's quite normal here. I have spent many happy days organising large mailouts. It's a boring job that can be made quite a social event - take 1,000 envelopes, five people and a large pot of coffee, then get stuffing!