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Publication 28 - Postal Addressing Standards >
2 Postal Addressing Standards > 23 Delivery Address Line > 234 Suffixes
The suffix of the address should conform with the standard suffix abbreviations listed in the ZIP+4 file (see Appendix C).
If an address has two consecutive words that appear on the suffix table (Appendix C), abbreviate the second of the two words according to the suffix table and place it in the suffix field. The first of the two words is part of the primary name. Spell it out on the mailpiece in its entirety after the street name.