You may want to cut your own envelopes and to have them ready, just like the ones you buy, with the dried glue on one edge so you just have to lick it and close. I’m going to show you how to make your own envelope glue. This is the recipe:
Mix three parts of white glue, like Elmers with one part white vinegar. Very easy. You can even keep this mixture in a closed container for future use.
Now, using a brush, apply this mixture to the edge of the envelope and let it dry. You may want to apply a second coat.
The envelopes are going to be ready to seal, no mess!