what is printed on the INNER envelope of a wedding invitation?

....and is this mandatory??

it's not mandatory ... it's supposed to prevent the envelope from getting damaged in the mail ...but mail delivery is pretty good and you shouldn't have problems regardless.

IMO it's a complete waste .... which is why i am not using them ... it saves me money, and it saves some trees

I think just the first names:

Outer: Mr & Mrs Smith

Inside: Bob and Jane

They are not mandatory

no its not mandatory. I didn't have them and no one noticed. What usually goes on it if you are inviting someone with a guest and don't know the guest name or if the guest does not live in the same place as the person you are inviting. I hope that makes sense

the outer would say Mr. and Mrs. Brad Pitt

the inner can say:

Mr. and Mrs. Pitt

or

Brad and Angelina


Also, if you are inviting someone with a guest just address the outer to that person and put 'and guest' on the inner.