Please would someone explain the intrinsic difference between Subscriber ID and Subscriber Key in Marketing Cloud for my better understanding.

2 Answers 2


Subscriber ID is a system defined unique identifier representing a Subscriber.

Subscriber Key is a user defined unique identifier representing a Subscriber.

  • just to add on, Subscriber Key is usually, by default, the email address of the subscriber. Oct 17, 2016 at 12:06
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    It's not best practice to set the email address as the Subscriber Key for a couple of reasons: (1) if the Subscribers email address changes, you can't change the Subscriber Key, so you will end up with duplicate subscribers, (b) there could be situations where you have subscribers with the same email address (e.g. a husband and wife that share the same email address). I'd recommend setting the Subscriber Key to a unique value like member number. Oct 17, 2016 at 20:58
  • @MarkDakyns if this answers your question, please mark the answer as accepted for the benefit of others. Oct 18, 2016 at 20:37
  • @EliotHarper In regards to your comments on reason 1: Here in Australia, the law requires us to not edit a current subscribers details, but to create a new subscriber account, as double opt-in is required. So, if a client wants to change their email address for a subscriber list they belong to, they have to re-subscribe, get the opt-in, and then confirm that opt-in as a valid request, via double optin process. It is up to that client to unsubscribe the old email. SalesForce actually recommended to us (in official training) to use the email address as the subscriber key.
    – ProxiBlue
    Nov 16, 2016 at 3:13
  • @ProxiBlue, the Australian 2003 Spam Act does not explicitly require a double opt-in process for email (although this is regarded as best practice to ensure that you have express consent). Either way, it's not best practice to create duplicate Subscribers for the reasons that I explained earlier. I'm unsure why Salesforce would be recommending this, perhaps its due to the fact that you are charged for each Subscriber, as a subscriber is counted as a Contact for billing purposes. Nov 16, 2016 at 21:08

To add on @Eliot Harper's answer: Careful when you use anything else than the Salesforce ID (i.e. Contact ID, Lead ID, etc.) as your Subscriber key. If you use Salesforce - the choice is clear. If you still don't use Salesforce and you plan a migration to Salesforce - do the migration first, then start using Marketing Cloud.

Changing a Subscriber Key later will involve Salesforce's support at a great cost!

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