How is the Delivery Point determined?

If only it were that easy to determine the Delivery Point. In many (if not most cases) the Delivery Point contains the last two digits of the primary number, but there are also a significant number of cases that don't adhere to that pattern. The USPS has them spelled out here specifically on page 37.

Here are a few examples:

Standard Delivery Point determination using the last two digits of the primary number:
260 Gilbert St Mansfield MA 02048 ==> 02048205160

Secondary number has a letter in it:
631 East St Unit E103 Mansfield MA 02048 ==> 02048296053

This is determined by taking the secondary number "E103" and using the USPS assigned value of 5 for the letter "E".  Multiply that value by 10 and then add the last number in the string, which is 3.  Take this value which is 53 and divide by 100.  The result is .53.  Thus the Delivery Point is "53".  (See page 43 of the referenced document)

There are many exceptions to the general rule and the USPS has addressed every possible exception. Since our service is CASS certified (meaning we are authorized to use the same data that the USPS has) it means that we are using the proper calculations to ensure that the Delivery Point code is accurate.

In short, ALL SYSTEMS NORMAL.