What is a Suppression List?
A suppression list is a collection of encrypted email addresses that an advertiser has marked as not to be used for email marketing. This list usually consists of consumers who have unsubscribed from receiving email promotions from the advertiser.
If you promote via email marketing, you need to take these suppression lists into consideration.
How Does the Suppression List Work?
If you are a publisher who wishes to send campaigns via email (e.g., in a newsletter), you must ensure that the email addresses on the advertiser's suppression list are excluded from your emailing. You can do this through the MyDaisycon publisher interface.
Anonymous Email Addresses for GDPR Compliance
All email addresses in our network are anonymized using an MD5-hash to comply with GDPR regulations. This ensures that a particular email address always results in the same hash, while making it impossible to reverse-engineer the original email address. This approach allows you to safely compare the advertiser's suppression list with your email list, ensuring compliance.
This method makes it possible to check if there are any email addresses that should not be contacted. The MD5-hash is one-way, ensuring safe and reliable use.
How to Use Suppression Lists as a Publisher
Follow these steps to ensure compliance when emailing:
- Prepare your email campaign and obtain permission from the advertiser via the Tools | Email Approval Tool.
- In MyDaisycon, navigate to Tools | Suppression Lists to check if a suppression list exists for the advertiser(s) you plan to work with. In some regions, multiple advertisers may be combined into one list.
- If a suppression list is available, download it. The output will be in MD5-hash format.
- Create an MD5-hash of your email list and compare it with the advertiser's suppression list. Deduplicate matching addresses to avoid emailing unsubscribed recipients.
Important: Always download the latest suppression list before emailing, as advertisers may update the list periodically.
With email approval and suppression list verification completed, you are ready to proceed with sending your campaign.
How to Create MD5 Hashes from your Email list
There are multiple methods for turning email addresses into MD5 hashes. While there are online tools available, we recommend using a local script to ensure data security. Below are two examples:
Example 1: Using PHP to Create MD5 Hashes from CSV Files
Download the advertiser's suppression list from MyDaisycon as a CSV file. You can then match and deduplicate hashes. Use the following PHP script:
<?php $skipHeader = false; $source = 'example.csv'; $column = 0; $destination = 'example-md5.csv'; $delimiter = ';'; $enclosure = '"'; $newLine = "\r\n"; $readHandle = fopen($source, 'r'); $writeHandle = fopen($destination, 'w'); if (true === $skipHeader) { fgetcsv($readHandle, $delimiter, $enclosure); } fputcsv($writeHandle, ['email', 'hash'], $delimiter, $enclosure); while (false !== ($row = fgetcsv($readHandle, $delimiter, $enclosure))) { $email = $row[0] ?? ''; $hash = md5($email); fputcsv($writeHandle, [$email, $hash], $delimiter, $enclosure); } fclose($readHandle); fclose($writeHandle);
Example 2: Using Microsoft Excel or Google Sheets
You can also use Excel or Google Sheets. Use the script below:
function MD5(input) { var rawHash = Utilities.computeDigest(Utilities.DigestAlgorithm.MD5, input); var txtHash = ''; for (i = 0; i < rawHash.length; i++) { var hashVal = rawHash[i]; if (hashVal < 0) { hashVal += 256; } if (hashVal.toString(16).length == 1) { txtHash += '0'; } txtHash += hashVal.toString(16); } return txtHash; }
Insert this script into your script editor:
- MS Excel: Click on the 'Developer' tab and go to 'Visual Basic'.
- Google Sheets: Go to 'Extensions' | 'Apps Script' or visit script.google.com.
Save the script, authorize if needed, and use the function MD5()
in your spreadsheet, such as: =MD5(A1)
. Make sure not to use uppercase letters, as they create different hashes.
Once you have the MD5-hash, you can compare it with the advertiser's list and deduplicate any matching addresses to avoid sending unwanted emails.
Note: The scripts provided are examples only. Daisycon is not responsible for their usage.
For more information about email marketing best practices, visit the following FAQ: Code of conduct for e-mail marketing at Daisycon.