DR. and Mrs. Smith, or Dr. and Mr. Smith, depending on the genders of the couple, but, in the second case, you might want to use the form Dr. Smith and Mr. Smith since men easily get their shorts in a knot over being upstaged by their spouses (or by anyone, for that matter).
If the couple are same-sex I would suggest always separating the names: Dr. Smith and Mr. LeBlanc or Dr. Smith and Ms. Leblanc.
Comment
Contrary to the opinion of the poster above, men of education do not "easily get their shorts in a knot", where etiquette dictates proper form. If they do, perhaps it is time to upgrade your circle of associates.
Just by Mr & Mrs , or by their professional titles , if any.
The proper way to address a mailing envelope is to place the stamp at the top right corner, add the senders return address on the top left corner of the envelope with the recipients full name and address in the middle of the envelope.
Mr. Robert Pollack, PhD.
Mr John Doe and family
The proper way address them is Mr. or Mrs Last Name
Addressing an envelope to a male child use to be 'Master', but now it can be Mr.and the female Miss.
* Senor & Senora ____________________. Senorita is single, Senora is married.
The proper way to position a label on a large envelope is to place the label in the same spot where you would place the recipients address. However, be sure the label is put on straight and not lop sided.
The proper way to address an envelope to a doctor office is to first input the name of the clinic. On the second line you can insert in care of or C/O with the doctor's name. On the third and fourth line you can insert the address, city, and zip code. Include any suite or floor numbers of the doctor's office on the third line.
Say there last name was "Smith" you would write Mr. and Mrs. Smith.
Use a complete return address, including department name, on all outgoing mail to be metered.Address envelopes so that the destination address is parallel to the longest edge of the envelope. Address large envelopes so that the flap is on the right or leading edge of the envelope. Seal all large envelopes.
A correct way to address an envelope to Spain is: Senor (Mr.) Senora (Mrs.) or Senorita (Miss.)