Most stamps and envelopes (at least here in Canada and I'm sure elsewhere in the World) are already self-adhesive. Just peel and stick. No licking at all. I do hate depositing cheques into the bank machine. You have to lick those to seal them. Yuck.
After spending a week at the headquarters of Hallmark and touring the factory where they make the cards and envelopes I can safely say don't worry about the envelopes from there. That place was so clean you could eat off the floor.
Now some of the stockrooms I've seen in stores.....