MLA

Wolff, Helen, 1906-1994. Postcard. Box 47, folder 1491. n.d.. https://collections.library.yale.edu/catalog/31907653.

APA, 6th edition

Wolff, Helen, 1906-1994. (["Box 47, folder 1491"])(n.d.)[Postcard]. https://collections.library.yale.edu/catalog/31907653.