Furthermore, in the Fall 2007 issue of Gluten Free Living, Amy Ratner reported, "There are actually only a few envelope glue manufacturers in the United States. National Starch & Chemical, a New Jersey company, is one of the largest adhesive suppliers in the world. A company spokesperson says it makes its glue from corn, which is gluten free."
As for stamps, a Post Office spokesman told Ratner there's no gluten in stamp glue either. At any rate, the ingredients in stamp adhesives are much less of an issue, since the vast majority now have pressure adhesive glue and can be pressed onto your mail without the need to lick them.