On campus there is a Mailboxes Etc. where you can send items via UPS, FedEx and USPS. Stamps and money orders but you must pay in cash. There's a Post Office next the College Park Metro Station. Hours are 10 am until 4 pm.
Use the US Post Office web site to find your nearest Post Office.
Graduate Student Life Stamp Student Union 1121A Graduate Student Suite College Park, MD 20742 (301) 314-9544 Phone (301) 314-9634 Fax yckim2@umd.edu