Boston Marathon confirmation postcards typically arrive anywhere from the beginning of November to the end of December (arrival dates may vary depending on production timelines and delivery destinations). Please note that your confirmation postcard is simply an additional notification of your acceptance into the Boston Marathon, and you do not need to bring it with you to claim your bib number on race weekend. Boston Marathon Registration Bibs When will I receive my confirmation postcard in the mail for the Boston Marathon? Do I need to have this document to claim my bib in April?