Wedding invitations were once delivered by hand. If you were a bride back in those days, your footman delivered your invitations to your guests’ homes. Their servants received the invitations and removed them from their mailing envelope, an envelope much too pedestrian for your guests to handle themselves. The servants, then, presented the invitation to your guests in its pristine inside envelope. Because the invitations were already at their destination, the inside envelopes had only the names of your guests written on them. The address was no longer needed. They just had to be directed to the appropriate members of the household.
Wedding invitations are still occasionally sent in two envelopes, but it has become more typical to only use one nowadays. Either way, the outside envelope is the mailing envelope. No abbreviations are used. Full state names, Rural Route and Post Office Box and any other Street/Avenue abbreviations are always written out.
Your guests’ names and addresses are written on its face. The copy may be centered or staggered. Staggered copy was much more popular years ago before there was such a thing as zip codes and before it was necessary to include the state on invitations sent in-state. Now, the addition of states and zip codes has, in most cases, made the last line too long to be staggered.
If using two envelopes, your guests’ names are repeated on the inside envelope. This time, however, only their titles and surnames are used. If children under the age of eighteen are invited, their first names would appear on the line beneath their parents’ names. If using only one envelope, it is important to list the name of all persons invited as well as specifying if any “guests” are also invited.
It is worth the time and effort it takes to prepare your guest list in a full way – especially if you are having calligraphy done or are having your envelopes printed with your guests’ addresses. There are etiquette guidelines for how to properly word the guest name line(s) including single guests, married/divorced guests, families, doctors, officials, etc. And when having your envelopes printed, organizing the information in a particular way will ensure each envelope is perfectly printed.