Feature: Native Mailchimp Integration — Audience Sync + Group Tags

[mbyrdLCS]

Summary

Add a native Mailchimp integration to B1 so churches can connect their Mailchimp account and keep their audience automatically in sync with B1 — the same way many leading ChMS platforms handle it today.

Why this matters

For churches: Many churches already pay for Mailchimp and use it to send newsletters, campus emails, and pastoral communications. Right now there is no automated way to keep Mailchimp in sync with B1 people data. They either maintain it manually or lose that sync entirely when switching to B1.

For ChurchApps: B1 already has a built-in group email feature (SendEmailDialog → MessagingApi). Every email sent through that costs ChurchApps money. If churches can route bulk email through Mailchimp instead, those sends shift to an infrastructure the church is already paying for — reducing ChurchApps' per-email cost at scale.

Many leading ChMS platforms have this built in natively and churches expect it as a standard feature.

How it would work

Settings

• B1 Admin → Settings → Integrations → Mailchimp
• Church enters: Mailchimp API key + Audience ID + server prefix (e.g. us14)

Automatic sync (via B1 webhooks)

When a person is created, updated, or removed in B1, the change is pushed to Mailchimp:

B1 field	Mailchimp field
First / last name	FNAME / LNAME merge fields
Email address	Subscriber email
Campus	Mailchimp tag (e.g. Campus: Bedford)
Membership status	MSTATUS merge field
Group memberships	Mailchimp tags (e.g. Group: Worship Team)
Person removed	Subscriber archived (not deleted)

Group-based tags

When a person is added to or removed from a B1 group, their Mailchimp tags update automatically. This is the key feature — it lets churches segment Mailchimp campaigns by B1 group without any manual list management.

Initial bulk sync

A one-time endpoint to push all existing B1 people into Mailchimp on setup day.

What this replaces

Churches migrating to B1 from other systems often have an existing Mailchimp sync where specific lists map to Mailchimp tags. This feature ensures that sync continues with B1 groups and campuses as the source of truth — no manual rebuilding of audience segments.

Discovered during

A church migration to B1 (July 2026). The church actively uses Mailchimp for:

• Weekly newsletter (≈5,900 people)
• Campus-specific lists
• Ministry-specific lists (students, kids primary contacts, etc.)
• Pastoral email (separate opt-in segment)

This came up during the migration and is a blocker for the church being fully independent of their previous system.

Note

A standalone proof-of-concept (b1-mailchimp-sync) has already been built and tested as a Vercel service. It handles person sync and campus tags. The group → tag piece and the in-app settings UI are what's missing from a native B1 implementation. Code: https://github.com/mbyrdLCS/b1-mailchimp-sync

[mbyrdLCS]

Proof-of-concept code

A working implementation is available at: https://github.com/mbyrdLCS/b1-mailchimp-sync

Built during the One Church onsite (July 2026) as a standalone Vercel service. Jeremy can clone it and run it — all credentials go in environment variables, nothing is hardcoded.

What's already working in the POC:

• Person create/update → Mailchimp upsert (name, email, campus as tag, membership status as merge field)
• Person deleted in B1 → archived in Mailchimp (not permanently deleted)
• One-time bulk initial sync endpoint (POST /api/sync/initial)
• Webhook signature verification

What's missing for a native B1 implementation:

• Group membership → Mailchimp tag sync (when someone joins/leaves a B1 group, their Mailchimp tag updates automatically)
• In-app settings UI in B1 Admin (Mailchimp API key + audience ID entry)
• That's it — the core sync logic is proven

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Cost savings context

One Church sends to ~5,900 people on their weekly newsletter alone. Across 20,000+ churches, bulk email routed through ChurchApps' own MessagingApi represents a significant per-send infrastructure cost. Churches already paying for Mailchimp — which is most of them, it is the most widely used church email tool — could route their bulk sends through Mailchimp instead, shifting that cost entirely to a subscription the church is already paying for.

PCO has had native Mailchimp sync built in for years and churches expect it as a standard ChMS feature. It is consistently one of the first questions asked during any PCO→B1 migration.