As part of how to address invitations etiquette, there are certain guidelines for the inner (inside) envelope if your wedding invitations come with two envelopes. Typically double envelopes come with more traditional styles.
Your inner envelope is the one that can have a colored lining for an extra charge, if you choose, and will hold your invite as well as any insert cards. Since it will be placed into the outside mailing envelope, it will come with an ungummed flap so it remains unsealed.
It is recommended that you address your envelopes before inserting your wedding invitations. This avoids having an uneven writing surface and prevents any indentations on the invitations.
Remember, both of your envelopes should be addressed in handwriting versus using printed or typed labels. The handwriting on both envelopes should be by the same person and be in one ink color, either black or blue, so everything matches.
On this inside envelope, first names and addresses are omitted. It is simply addressed “Mr. and Mrs. Smith”, as an example.
All invited family members should also be included, however it is best NOT to use the words “and family.” Instead, list all guests’ names keeping in mind that names of children may be spelled out (for example, “Jane and John”) and written below the parents’ names in order of age.
Couples who are dating should each receive their own invitation instead of writing “and guest” on the envelope. It is up to you to find out each guest’s name.
You may address close friends and relatives informally on your inside envelopes as appropriate. If your verse wording lists you as issuing your wedding invitations, addressing relatives as “Uncle Fred,” “Grandma Smith” or “Grandpa” are all acceptable. If parents are inviting the guests, they would not refer to the uncle of the bride as “Uncle Fred.”
Follow this link for how to address wedding invitations on the outside for mailing.