List Cleaning with MD5

Download MD5 Conversion Utility

MD5 is a one-way encryption process developed by Professor Ronald L. Rivest of RSA Security. Email addresses that have been encrypted into MD5 format cannot be unencrypted, even by the person who originally performed the encryption. However, an email address encrypted with MD5 will always result in the same character string. Therefore, two lists of email addresses that have been encrypted with MD5 can still be compared with each other to determine if there are any matching records.

Emailers can take advantage of MD5 to allow for the comparison of a suppression list against a mailing list without sacrificing the privacy of one party’s list data.

Following is a suggested method of using the MD5 conversion utility to clean a publisher’s mailing list of all addresses on an advertiser’s MD5 formatted suppression list.

1. Download the advertiser’s MD5 suppression list.
2. With your mailing list, create a delimited text file that includes each email address in two columns.Example: user1@mail.com, user1@mail.com
   person1@yahoo.com, person1@yahoo.com
   jeff@address.com, jeff@address.com
3. Use the MD5 conversion utility to convert one column of your mailing list to MD5 format.Example: user1@mail.com, 73dbb4ed51752f4d60afaeec8c9733e8
   person1@yahoo.com, b584a1e82ecc5b70cc6343b7d6d150ad
   jeff@address.com, 641a3585d3589304eab6c5bd37b1761b
4. Compare the MD5 column of the mailing list created in step 3 with the suppression list you downloaded in step 1 to find all matching MD5 records.
5. The resulting list of matching addresses will be a subset of your original mailing list, still showing both the email address and MD5 formatted address.
6. Simply remove the MD5 column from the list of matching addresses, and you now have a plain text list of email addresses that must be removed from your mailing list prior to delivery.