Mail Stop Codes
The mail stop is used to identify a location of each department and office – it is not intended to identify personnel. Each department or field office has been assigned a 4-digit mail stop equivalent to the Zip Plus 4. If you do not provide mail stop codes for internal mail, it may not be delivered in a timely manner, mis-sorting could occur, or it could be undeliverable as addressed. If mail does not have a mail stop code or department, mail services will identify the recipient's department and forward accordingly.
Use mail stop codes as a part of your return address for internal and external mail.
Access the complete list of mail stop codes for each department.