addressing envelopes

I really do not want to address the outer envelopes as Mr. and Mrs. John Smith! That just seems so formal to me and it offends my feminist sensibiities. Are there any other options? Can I do Mr. and Mrs. John and Mary Smith? Or even John and Mary Smith? We are doing the inner envelopes informally- John and Mary or Uncle John and Aunt Mary etc.. .

Look what I just found on theknot.com...

-- Married couple, traditional:

Mr. and Mrs. Harold Paris
92 Pacific Avenue
and so on...

-- Married Couple, modern:

Harold and Emma Paris
92 Pacific Avenue
and so on...

-- Married couple, different names, or unmarried couple, living together:

Professor Connie Chideya
Doctor Darren Duncan (list the names in alphabetical order)
18 Blueberry Road
and so on...