At least since the 1400's and probably much earlier.
glue it is a type of glue activated by liquid (your spit)
Wax is NOT a good substance for glue, it can seal things such as envelopes, but will not actually glue anything.
horse hooves and bone.
Most envelopes are pre-glued with 'gum arabic'
Envelopes have a strange taste when you lick the seal because there is a layer of glue there. The glue is made from gum arabic. Gum arabic is produced with the sap of acacia trees.
The taste is not harmful, but it does mean you have a good sense of taste.
They like the glue on envelopes. Do not lick the glue!
With self-sealing envelopes, all one have to do is to remove the protective tape from the flap and close the flap down for a secure seal. It differs from other envelopes in that it doesn't require glue to seal the envelope so it is more convenient.
No, if you are referring to the ones you lick, they use a Casein-based glue.
Most glue is sticky to the touch, as this is part of its function. However, various glues and adhesives may not feel sticky, and only adhere through the addition of heat (hot glue), moisture (envelopes), or pressure (glue dots).
Take the rollers out and wipe them with a rag containing Goof Off.
Print carefully, don't press too hard, and you'll be okay.