Interdepartmental Mail, also known as Campus Mail, is a service that specializes in delivering mail to buildings on campus. It’s best known for delivering those brown envelopes with the string ties. Envelopes can be filled with a variety of materials - please, no breakables or non-work-related items. It's not associated with the U.S. Post Office, so Interdepartmental Mail does not require postage. The Campus Mailroom receives thousands of pieces of mail each month so it’s important to accurately address and organize outgoing mail. Some tips.