How to Address an Envelope Using C/O
When sending mail to someone who has another primary address but wishes to accept mail at a different address, the envelope must be addressed with an "In Care Of" line, most often abbreviated "C/O." The "In Care Of" line includes the name of a primary resident or the primary entity at an address. If the intended recipient is staying with a relative, for instance, the relative's name would be used; if it's a hotel or hospital, that name would appear in the "C/O" line.
Write the addressee's full name near the center of the front of the envelope. This is the first line of the address.
On the next line, write "C/O" and the full name of a person who is a primary resident at the mailing address, or write the name of the business or entity at the location.
Add the street number and street name on the next line.
Write the city, state abbreviation and ZIP code on the fourth line.
Write the name and full address of the sender in the top left corner of the envelope.