Suppression List suppression method - Subscriber Key or Email Address?

Question

My business has some commercial arrangements which prohibit curtain customers from being contacted about certain products. I'm thinking that the best way to exclude them will be through a Suppression List.

Before I do this, can someone confirm if this method will suppress contacts by Email Address or SubscriberKey? I know that if I use a DE it is SubscriberKey but is that the same for Suppression Lists?

Normally, I would use Auto-Suppression but it's too fiddly when there only some circumstances when we cannot contact them.

Answer 1

Suppression Lists' schema cannot be modified and they always come with both Email Address and Subscriber Key field.

Auto Suppression Configurations on the other hand work by email address exclusively.

About Suppression lists:

So, if you have Subscriber Key enabled, do they use subscriber Key or Email Address? ->

The answer is Subscriber Key.

This is documented explicitly in a bit of an odd place, namely in field level encryption:

https://help.salesforce.com/s/articleView?id=sf.mc_overview_faq_use_suppression_lists.htm&type=5

Suppression Lists

Use subscriber key values to suppress subscribers in Marketing Cloud Security and Encryption products.

Can I still use suppression lists [when using field level encryption]?

You can use subscriber key values to suppress subscribers

Suppression Lists use subscriberKey, that documentation just confirms they would even do so after you encrypted said key.

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Additional evidence:

1. implicitly, the documentation also mentions it in the "right" location as it says

A suppression list is a list of subscribers

https://help.salesforce.com/s/articleView?id=sf.mc_es_suppression_lists.htm&type=5

...and subscribers are defined by their Key.

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2. Also, this document here

https://help.salesforce.com/s/articleView?id=sf.mc_as_query_find_subscribers_on_a_publication_or_suppression_list_ref.htm&type=5

shows what the data structure of a suppression list is, when it instructs on how to mirror data inside it into a data extension. Subscriber Key is the primary key, email is not. This alone doesn't prove anything, but it is consistent with the descriptions above and makes perfect sense with subscriber key being used for the suppression: