Any time two members of a married* couple have different names, you list each one separately, joined by “and”. Contrary to over-simplified popular assumption, the “ladies first” rule does NOT apply in all situations. People’s “business name”, “formal name” and “informal name” are all different. Each one is supposed to be used in the right situation.
An envelope being sent through the public mails is a business document. Business names comprise title, given name or names and/or initial or initials. On an outside envelope mailed in the Engish-speaking world, outside the United States you would therefore use:
“Ms Mary Smith-Jones”
The names of the actual invitees will be clarified on the invitation write-in line or inner envelope. In the overtly egalitarian United States where husbands presumably are considered equally likely as wives to manage the family social calendar, the outer envelope would use:
“Mr. Michael Jones and Ms. Mary Smith-Jones”
— mote the periods after the titles consistent with U.S. usage. The gentleman’s name goes first so that he can “protect” his lady and “make way” for her in this dangerous public business environment (snort — I am at least as competent to make my own way as most gentlemen I know, but it’s nice to leave the gentlemen their illusions).
Formal names consist of the title and the surname only. On an inner envelope or formal invitation write-in line, you would use:
” Mr Jones and Ms Smith-Jones”
As above, formal situations are considered public, so the gentleman “takes point” just in case there are social snipers or etiquette landmines to be overcome.
Informal names consist of the primary given name or names, only. On an informal invitation you would use:
“Mary and Michael”
Informal situations are considered private and intimate, and therefore safe, so the gentleman steps back and lets the lady go first.
“Mr and Mrs Michael Jones” is correct only when the gentleman’s business name is “Mr Michael Jones” and the lady’s business name is “Mrs Michael Jones”. Very few modern ladies style themselves in that way, but it is perfecty correct, and used to be the norm. My mother signed letters “Mrs Nestor Phipps” even though her given name was not — thank goodness! — “Nestor”. In fact, traditional etiquette allows the title “Mrs” to be used only before a man’s name: either the husband’s surname, or the husband’s given name followed by his surname, or the father’s surname followed by the ex-husband’s surname. All other usages require either “Ms” or “Miss” if you are choosing to follow traditional proper form.