Documentation
Group segregation vs. Mailchimp audiences
Membership organisations rarely have one flat list of contacts. A member is usually in several groups at once — a branch, a region, a committee, an executive role — and each needs to be emailable independently, without one group's opt-outs or billing leaking into another. Mailchimp's audience model wasn't built for that. This is what Postrider does instead.
One subscriber record per person
Postrider tracks a single subscriber record per email address, account-wide. Being on five lists doesn't create five billed contacts — it's one person with five independent list memberships. Mailchimp's audiences are separate contact pools by design, so the same person appearing in three audiences is billed as three contacts.
Two layers of status, not one
Every subscriber carries a global suppression state — set when an address hard-bounces or files a spam complaint — which applies account-wide, overriding every list. Layered on top of that, each list membership has its own independent subscribe state. Unsubscribing from one list flips only that list's state; every other list membership is untouched.
Lists that populate themselves
Rather than manually maintaining membership per list, a list can be configured with a sync rule against a real membership source — a Joomla user group, a Community Builder field value, or any database table. As membership changes (someone joins a branch, changes role, or leaves), the lists they belong to update automatically, both on save and via a scheduled resync as a backstop.
Why this matters in practice
Consider someone who is both a member of a specific branch and holds an executive role across a whole region. They should receive both the branch's list and the executive list, be billed once, and be able to leave the branch list without it affecting their executive-list membership — and if their role changes, both lists should update without an administrator manually re-adding or removing them. That's the ordinary case this model is built around, not an edge case bolted on afterwards.
Related
See the full Mailchimp comparison, or back to the getting-started guide.