Demystifying Subscriber Key

This may be the first Marketing Cloud post ever written here at but, the subject has certainly come quite often and I think I should share some thoughts.

What the Subscriber Key should be set as? and shall one change it?

In Marketing Cloud one has the concept of Subscriber Key:

A subscriber key is a text field that contains a value that uniquely identifies a subscriber in your Marketing Cloud account. Marketing Cloud Connect uses subscriber key to identify the Sales or Service Cloud record associated with the tracking data returned from the Marketing Cloud.

Essentially it’s a unique identifier for each one of your subscribers. In a sense is external driven identifier to be a subscriber identifier in Marketing Cloud, as you can set it up when you add a new subscriber.

Anyone you will ever communicate with using Marketing Cloud will end up in the All Subscribers List with a Subscriber Key, which you can access from the Email Studio tab.

Often you see that the Subscriber Key is mapped with Salesforce ID, if you manually import subscribers into Marketing Cloud Salesforce recommend to create a custom formula field for Contact and Lead records to generate an 18-digit ID, based on the Contact ID or Lead ID. Use a text field and input “CASESAFEID(Id)” as the formula, with the Contact or Lead ID in parentheses. When exporting data out of Sales or Service Cloud to import into Marketing Cloud, include this value to use as the subscriber key.

But I have also seen the email used as Subscriber Key quite an often. So the question on what it should be and if migration is required? That is what Im going to try to answer here.

If you use email as subscriberKey, Email Can Only Exist Once

If you use other unique ID as subscriberKey, Email Can Repeat But Not the Unique ID

Lets look at how Marketing Cloud process both options on send:

Screen Shot 2019-06-11 at 12.05.39

Screen Shot 2019-06-11 at 12.06.01

Conclusion, it doesn’t matter!

a) Well, if you are starting from scratch and you are using the Connector to Salesforce then mapping with Salesforce ID is a good idea, for ease more than anything.

b) And well, we must admit that using Email as Subscriber Key over time these values in some rows may not match as we know people changes their email address.

c) You can make up your own too, any odd DI, whilst ideally you keep it consistent.

** but in my mind please please please do not spend a lot of time and money to remap Subscribers Key as it requires Marketing Cloud support and premier services.


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