The applicant union filed an application for certification and delivered it by placing it in the responding party's rural mailbox.
The union organizers accidentally raised the mailbox flag, causing the letter carrier to pick up the application and place it in the mail system.
The responding party did not receive the application until later.
The Board found that placing the application in the mailbox constituted valid delivery under the Rules, as it was the customary location for the business to receive documents.
The Board extended the time for the responding party to file its response and found no significant prejudice.