Gina is correct. Those are fine envelopes to use.
Once you put the cuttings and moss or wet paper inside of a ziplock bag, you can just wrap in crumbled newspaper and shove in those regular envelopes, I received packages in them and they work fine. I like recycling, so I send the same envelope out again, it handles many trips, if you prepare the packages at home, put the zip lock bag inside of a bread plastic bag and fill with shread paper.. then just put the whole thing in the regular envelope or the flat rate works best for many cuttings as the weight does not matter.