It is important to understand the difference between a data source and mailing list/subscription list.

Data Sources

A data source is a list of actual profiles that can contain names, addresses, phone numbers, and other personal information about the individual it is associated with.

Such profiles can be created via file upload (CLIENT data sources) or live data feed (PMS and WEB data sources). Multiple PMS profiles for the same individual can be merged, and profiles for the same individual from different data sources can be matched. See Global Profile for more information. 

Mailing Lists/Subscription Lists

A mailing list, also referred to as a subscription list, is simply a list of email addresses and opt-in status for those addresses. No personal information is stored in a mailing list.

A Subscription Center is required in order to set up mailing lists, and guests use the Subscription Center to manage their subscription preferences.

Email Address

Because there is no profile information contained in mailing lists, they are data-source agnostic: an email address that is present on a single mailing list can belong to any number of profiles, in any number of data sources. This means that every profile that shares a given email address also shares the same subscription statuses for each of your mailing lists.

Opt-In Status: Single and Double

Mailing lists store the opt-in status for emails that are included in them; the specific statuses depend on whether you are using single opt-in or double-opt in.

Single Opt-In
Each email address associated with a mailing list has a status of either Opt-In or Opt-Out.

Double Opt-In
Each email has two statuses: the first one is Opt-In/Opt-Out, just like above, and the second one is Pending/Confirmed. This second status is tied to clicking the #DOUBLEOPTINLINK# which is sent to the guest as part of the Double Opt-In process.

Global Subscription Status vs Mailing List Subscription Status

Each email address has one Global Subscription Status, which is the value we see in the Email Status tab in an eInsight profile: Valid, Unsubscribed, Bounced, etc. This status is not targeted directly in campaign criteria, but rather using checkboxes in the Campaign Settings dropdown of the Criteria tab in the editor (Include Unsubscribed, Include Bounced).

By contrast, an email address has a distinct status for each specific mailing list, which can be viewed in the Mail List or Subscription List tab of an eInsight profile. An email can be opted into or out of any combination of mailing lists, and these statuses do not affect global subscription status. Mailing list status is targeted in the audience builder using filters from the Subscription Center category.

A profile can be opted-out of every mailing list, but still have a global subscription status of Valid/Subscribed. This means that if the appropriate filters are not being used, this profile may still be included in audiences and receive communications they do not want.