A sympathy card to a widow should be addressed to "Mrs. Robert Smith," substituting Robert Smith with her deceased husband's name, according to the Emily Post Institute on etiquette. While the traditional etiquette for correspondence mandates the use of the husband's first and last name following the prefix, more modern publications suggest that it is up to the sole preference of the widow.
Real Simple Home & Lifestyle Network reports that while a widow retains the name of her husband until she marries again, some widows find it important in today's society to substitute their first name in lieu of their husband's name on letters, contracts, invitations and other correspondence. An example of this scenario would be to call the widow "Mrs. Jane Smith" rather than "Mrs. John Smith." Both are considered acceptable manners of addressing a widow in the 21st century. Occasionally, the question of how to address a divorced widow, a woman who is no longer married to a man at his time of death, arises when mailing letters. Technically, the woman is not considered a widow and should be addressed by the name she uses in current public interactions, whether it is her former married name, current married name or maiden name.