I found a really cool recipe and it does work quite well. Cardmakers will love this one. It's a recipe for envelope glue. It dries on the envelope just like commercial glue. The recipe is as follows:
6 Tablespoons of White Vinegar
4-0.1 ounce packets unflavored gelatin
1 Tablespoon Vanilla Extract
Bring vinegar to a boil, add gelatin and stir until it is dissolved. Add the vanilla extract and stir until well mixed. While still warm brush a thin layer onto the back of an envelope flap. Set it aside and allow to dry.
Store unused mix in a airtight container and to reapply the glue rewarm mixture and apply to envelope.