Can you please tell me what are the main arguments against using Email Address as Subscriber Key in SFMC? I have been getting requests from our internal stakeholders to use the email as Subscriber Key instead of looking for another type of ID, which I always recommend, but in the end I always lack a number of 'bullet-proof' arguments as to why using email as SK is not best-practice in Marketing Cloud. The only arguments I have used so far is that SF recommends against it, and that when a subscriber's email address is changed his/her SK would be still showing the "old" email address as SK.

  • Hi, you can find my answer here: salesforce.stackexchange.com/questions/326898/… Mar 10, 2021 at 10:30
  • OK, so you're saying that email address is PII so there's privacy issues and is constantly being changed by the customers themselves so there's the residual factor. Is there any other argument I can use besides the said two?
    – nix9247
    Mar 10, 2021 at 10:48
  • 2
    it's not unique and not persistent over time. Mar 10, 2021 at 10:53
  • In the context of how Marketing Cloud works, you'll end up with additional overheads that may not have been planned for. To update a subscriber in Marketing Cloud, you need their subscriber key. If you use email address as this key and a user changes their email address, you need to be maintaining that old email address somewhere in order to update the existing subscriber record, or else you will just create new subscribers, have multiple records for the same person and incur greater costs as a result. Mar 10, 2021 at 11:01
  • 1
    oh, and I'll add that email won't work multi-channel. Mar 10, 2021 at 11:52

1 Answer 1


I see four main points, when advising clients on what to use a Subscriber/Contact key. The details are indeed very much up to the individual scenario, but these points are universal. The Contact Key should be:

  1. Unique (daaah!)
  2. Persistent
  3. Channel agnostic
  4. (Global)

I have put a parentheses around number 4, I'll get back to that. So, your suggestion for using email address is failing 2 out of 3 checks. I don't think I need to explain why it's a good idea, that a Contact Key should be unique, so I will focus on the remaining points:

2. Persistent

We want the same ID to follow our subscribers/customers throughout their entire lifetime. This should apply to all the systems in your landscape. At least systems which to higher or lesser degree exchange data with Marketing Cloud (see item 4 below). Email address CAN be persistent, but as it is provided by the customer, it is nothing which we can ensure, and people tend to change their email addresses, especially in a B2B context. You don't want to see yourself map each update of email addresses to the initial email address provided by the person 5 years ago. This will easily lead to confusion and poor data quality.

3. Channel agnostic

There are markets around the globe, where emails is not a predominant communication channel. Mobile text messages are very widespread in e.g. Asia and Africa, and relying on email address as a contact key will make it difficult for you to create consumer identities from other channels than email. Also for app push notifications, you should not see the email address as a prerequisite. You might use phone number and a one off code sent in a text message for authentication purposes. Here, we also can't guarantee presence of an email address in the context of creating a new contact.

4. Global

Especially in complex system landscapes, where we are working with systems of various capabilities, it is not given that all of them have the knowledge of customer's email address. Another key is probably utilised, and hopefully there is an IdP solution in place, which has the central responsibility for managing the core identity details, such as names, contact information (phone number, home address, one or even more email addresses), and map all of this into a single identifier, which is then propagated across all the relevant applications.

There is another detail to keep in mind, in case you are using Marketing Cloud along with Service/Sales Cloud and utilising the Marketing Cloud Connector. In order to use the standard functionality it offers, of a.o. Synchronised Data Extensions and Salesforce Data Entry Event in Journey Builder, you need to use either Contact-/Lead- or User ID as your Contact/Subscriber Key. There are ways to work around that limitation, especially if you have a global IdP in place, and/or have only a limited subset of your contacts in Service Cloud, but this is beyond the scope of this post.

I hope this gave you some more background on what to be aware of, when deciding on Contact/Subscriber Key.

  • 1
    Nice :) something else that falls in the "global" category: various systems have different standards as to "what makes a valid email address", Sales Cloud and Marketing Cloud alone have two length limits currently. There are perfectly legit email addresses with umlauts, "+"-signs etc., that you cannot convince some systems to accept. Try to find "the universal regex to validate email addresses", you will find a million answers. Given that the only argument for email as key I can think of is - "it's in front of my nose" - save yourself all the longterm pain and use something else. :) Mar 10, 2021 at 17:12

Not the answer you're looking for? Browse other questions tagged .