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Address a group instead of naming every person. Courier resolves membership at send time and delivers one message per member. There are two kinds of group, and the difference is who decides membership.

Lists

You choose the members. Add and remove them yourself, and membership changes the moment you do.

Audiences

You write a rule about profile data. Courier keeps membership current as profiles change.

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Which one to use

Use a list when you cannot express the group as a query. Use an audience when you can, so you never maintain it by hand.

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Limits & behavior

  • Lists are exact, audiences are eventual. A list member is present the moment you add them. A large audience rebuilds over minutes, and sends read the stored membership, so let a rule change settle before a critical send.
  • MEMBER_OF is a send-time filter, not a group definition. Use it inline on the recipient to scope a send to one tenant. It is not part of a list or an audience.
  • Preferences still apply. Members who opted out of the template’s topic are recorded as UNSUBSCRIBED rather than delivered.