Linking spouse relationship information
Two things:


if you want to only send one e-mail to a couple in a relationship who prefer to share an e-mail - whether husband/wife, married LGBT couples etc - create a new Household and add both to it, add the shared e-mail address to the Household and search Contacts in that household without an e-mail address but a postal address - like this in Search Builder -  


Household Name IS NOT EMPTY ...AND...
Email IS EMPTY '' ...AND...
Contact Type - 'Household' . 


I would prefer to have an e-mail for each of a husband and a wife, each of two married partners of any gender, etc - I have my wife and I in Civi with our own separate e-mails and we are also linked to the same Household. Sending to both e-mails or just a shared e-mail for a contribution ask depends of course on the couple's preference.