Please email me for my lettering style sheet!
Before the 20th century, the postal service wasn’t very reliable. In fact, it was nearly nonexistent in certain areas. The only guaranteed way to deliver a wedding invitation was by hand delivery, usually sent by a hired courier or servant of the family. Since many of these deliveries were by horseback, the envelope might not arrive in the cleanest condition. Thus, the double envelope was designed. Once the courier reached his destination, he handed the invitation to the butler or housemaid, who then removed the outer envelope and handed the inner envelope along with the invitation to the master or mistress of the house. This is why it is now considered traditional to use the complete, formal name and address of your invited guests on the outer envelope of a double envelope set (or on the outside of a single envelope). –The Emily Post Institute