What Facebook Does with Your Email List When You Create a Custom Audience

Have you ever tried creating a Custom Audience on Facebook? Have you wondered what happens with the email addresses you upload to Facebook in the process?

In the light of Facebook’s ever-changing privacy policy, it’s reasonable for advertisers to have concerns about the data they share with Facebook – we recently spoke to Facebook to clarify the details.

First off, Facebook assures us that the email data is protected and is only ever used for the purposes of your advertising campaign. According to Facebook, when you upload a list of email addresses on the ad platform, your customer list is hashed locally on your browser before it’s sent to Facebook.

Hashing is a way of encrypting a piece of data into hexadecimal strings and it turns email addresses that you share with Facebook into a combination of random numbers and letters – if you’ve ever posted an ad on Craigslist, you might have noticed your email was converted into a string of gibberish to protect you from unethical behavior online. Similar encryption happens when you create a custom audience on Facebook.

When those hashed email IDs are sent to Facebook, they’re then matched against Facebook’s existing list of their users’ hashed IDs. This code cannot be traced back to the email address; yet, the behaviors associated with the email address can be recorded. The matches are then added to your Custom Audience. Matched and unmatched hashes are then deleted.

When you create a custom audience with your email list, it’s very rare to see a 100% match rate – in many cases, less than half of email addresses will be matched.

According to the report by Radicati, the average internet user has 1.7 email addresses, which means that most people have at least two email accounts. There’s no guarantee that the leads on your custom list used the same email when they set up a Facebook account.

In addition, 17% of Americans create a new email address every 6 months and 30% of subscribers change email addresses annually. This is why it might be difficult for advertisers to compile a high quality up-to-date email list that matches Facebook email data.

As an advertiser, you might also be concerned about the possibility of Facebook using your uploaded email addresses for other purposes, besides your advertising campaign. Facebook assured me that the site does not give out advertiser or client information to third parties – they only uses the email data you share with them to help you target your ads.

So there you have it – it’s good to clarify the exact details of such processes to ensure you can utilize such tools with peace of mind.

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