The basic requirements for 4C mailboxes are as follows:

  1. The post office MUST approve the location of where the mailboxes are installed. Always consult with your local post office before ordering or installing any mailboxes for your project. 

  2. No customer lock shall be over 67” from the finished floor.

  3. No mail slot shall be under 28” from the finished floor.

  4. ONE parcel locker for every FIVE mail slots. This is where there is some grey area. The local post office has the final say on how many parcel lockers are required for any project within their delivery area. They can require a ratio of up to 1:5, but not more. They can also allow less, but that is left to their discretion. 

  5. At least one customer compartment shall be positioned at a height of less than 48” from the finished floor. However, local regulations may override this and require 100% of the mailboxes to be under 48” from the finished floor. Check your local building code for the regulations in your area.

  6. No parcel locker compartment shall be under 15” from the finished floor. 

It is essential to contact your local post office during the planning stage of your project. Some post offices are more relaxed on these requirements than others and will allow exceptions to these rules. To find the contact information for the post office in your area please use the link below. 

https://tools.usps.com/locations