Determine membership in an SFMC list?

Question

We currently have two versions of our emails with one version showing rewards content and the other not. While we'll soon be combining the two, for now we still have them separated. As such, we are attempting to display content conditionally upon membership in a list. We will send email A to List A, and if the customer is also in List B then we will show content X, otherwise we will not. This is currently being handled with Ampscript for the email that's being sent to a data extension, by first determining via Lookup() if the customer's email address is in the target DE, and then by using simple IF...ELSE within the email body.

Answer 1

You can't use the Lookup functions to retrieve data from Lists. You could hack away and use AMPScript InvokeRetrieve against the ListSubscriber API Object - potentially through a Landing Page, but this wouldn't be advisable if this is for a mass send to many subscribers as you'd take a big hit on send speed and probably blow out your Super Message quota.

Preferable for large sends would be to pre-process your sendable data using a Query Activity. You might use something like this...

SELECT
    c.SubscriberKey,
    c.EmailAddress,
    CASE
        WHEN l.SubscriberKey IS NOT NULL THEN 1
        ELSE 0
    END AS InListB
FROM
    MyCustomerDE c LEFT JOIN
    _ListSubscribers l WITH (NOLOCK)
        ON  c.SubscriberKey = l.SubscriberKey AND
            l.ListID = 12345

Without knowing too much about your data it's hard to give you the actual SQL you need, but the principle stands - pre-process before sending for scalability.