Trust me, you are not alone. Most people have no idea where to start with wedding invitations! I work for wedding stationery company, so I could definitely help you with some of these questions!
Inner & Outer envelopes are mostly a formality that go way back in stationery ettiquette. These days, it’s really common for brides to only use one envelope (to save paper and cut costs, etc), while others love the idea because it’s very traditional.
The general idea is that the Outer Envelope (the mailing envelope), usually gets dirty or marked as it goes through the mail, and is generally torn open and thrown away. The guest is then left with a clean pristine inner envelope to hold onto in the long term, which is especially helpful if you have multiple enclosure cards, like a card with accommodations, directions or other important details. Everyone else is right, it’s pretty much just a formality that’s not really necessary…it just depends on your own taste and budget.
• Plus Ones & Addressing:
If you do use an inner envelope, that’s traditionally where you would note a guest. For example, if you were inviting your single BFF, and wanted to give her a date, you would address the outer envelope to “Ms. Jane Smith”, and then on the inner envelope, you would write “Ms. Jane Smith and guest”.
As everyone else mentioned, you can also just address the mailing envelope to include the names of the guests invited if you don’t do inners. You can also include a line on the response card (these two are probably the ones we reccommend most often):
____ of ____ guests will attend (you fill in the second line) or
We have reserved ______ seats in your honor
These are also a subtle way to let people know if the invitation will include their children (if they have two children and all are invited, you would put 4 and can address the envelope to “The Smith Family”.
I love Sweatergal007’s advice for addressing — that’s pretty much exactly how I did it too! I would just add that a good rule of thumb is that adults age 18+ get their own invitation (either as a couple, alone, or with a plus one). Anyone under 18 can be considered a child and included in the “family” group invitation.
Lastly, just some overall advice…if you happen to know that certain guests HATE their formal name, or prefer a diffrent title, do what makes them most comfortable. Etiquette is all about being gracious and courteous to your guests. At the end of the day, it’s your wedding, and you know yourself, your wedding style and your guests the best, so do what makes you happy.