Data that is inconsistent will prevent proper deduping -- for example, business names or department names entered in an address field instead of the address. The front line people entering data get pressed for time when they have customers on the phone and don't always have time to be careful about where data is entered or whether it is entered correctly. We recently processed a file where 1/3 of the data was either duplicates or undeliverable because of data entry errors.
Zip Codes change over time - is your database up to date? Having a wrong zip code on your mailing can delay delivery time or not be deliverable at all.
Some of the processes that we use to clean up databases are:
NCOA - Up to 20% of the population is in the process of moving each year. We will run the data through the National Change of Address software making sure new addresses are picked up. New postal requirements require NCOA to be performed if trying to qualify for postage discounts or to have "or current resident".
CASS - Coding Accuracy Support System - This system standardizes addresses and assigns zip+4 coding. Passing data through this process prior to deduping the file will help catch more duplicate entries.
DMA/NoMail - The Direct Mail Association maintains a list of people who want their names removed from mailing lists and do not want to receive advertisements in the mail. Removing these people from your database will help ensure you are not wasting money on postage mailing to people who don't want to receive it.
Deceased - Does your file contain names of people who are deceased? Nothing irritates families more than getting mail addressed to their family members who are deceased.
DBSLists.com can scrub your database before you mail.
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