One Click, All Lists: How an Email Publisher Plugged a Multi-ESP Unsubscribe Gap
How a solo financial newsletter publisher used Fillout and Zapier to sync unsubscribes across four ESPs instantly — closing his CAN-SPAM gap.
A solopreneur running a financial email newsletter had built his business on redundancy — a smart move for deliverability. He spread his subscriber lists across four email service providers (ESPs): Maripost, Brevo, Tiny Email, and AWeber. If one platform flagged his account, he could keep sending from another. The problem: when a subscriber clicked unsubscribe, that action only landed in one ESP. The other three kept sending.
The Problem
The publisher — a solo operator running two financial newsletters in the US market — ran his subscriber lists simultaneously on multiple ESPs as an explicit backup strategy. He knew platform risk was real: ESPs could flag accounts, suspend access, or experience outages. Multi-ESP was his insurance.
Every week, he exported active subscribers from his primary platform and re-imported them into the secondary ESPs. The process was manual and repetitive, but workable. What wasn't workable was the compliance gap.
When a subscriber unsubscribed from Maripost, the other platforms didn't know. They kept sending. An opted-out subscriber would continue receiving emails from Brevo, Tiny Email, or AWeber for as long as it took someone to notice — which might be never. This created two serious risks:
- Compliance exposure: continuing to email a subscriber who has opted out is a CAN-SPAM violation. For a publisher whose entire revenue depends on inbox placement and advertiser trust, a spam complaint escalation or platform suspension is not an inconvenience — it is a business continuity event.
- Deliverability damage: each complaint from a subscriber who thought they'd unsubscribed chips away at sender reputation across all platforms. The multi-ESP strategy designed to protect deliverability was being undermined by the very thing it was built around.
He had sat with the problem for over a year before booking a second consultation with Connex. He said at the top of the call: "I never resolved the issue. I need to understand how I can get this done."
What Was Built
Connex designed a centralized unsubscribe system covering both lists (Daily Market Alerts and Market Moving Trends) and all four active ESPs, built across three ZoomFlow work sessions totaling approximately four hours.
The architecture:
- A Fillout form embedded on the publisher’s website — one page per list. Each form is pre-populated with the subscriber’s email via a URL parameter in the email footer, so subscribers can only unsubscribe their own address, not someone else’s.
- A Zapier workflow triggered on form submission that fans out to all active ESPs in parallel. Each branch makes an API call to that platform’s unsubscribe endpoint. If one branch errors (platform outage, API hiccup), the others still execute.
- A custom branded confirmation page the subscriber lands on after submitting — replacing generic ESP confirmations with a consistent on-brand experience.
Two per-platform quirks surfaced during build. Brevo requires API calls to originate from whitelisted IP addresses; the Connex consultant worked with the publisher's Brevo support contact to open the necessary permissions before the Zapier connection could be made. Tiny Email's API requires a subscriber lookup step before the unsubscribe call — the consultant discovered this during live testing and adjusted the workflow on the spot.
The full workflow was tested end-to-end with real addresses across all three production ESPs during the session, with the publisher watching as each unsubscribe landed correctly.
Estimated Impact
No hard before/after metrics were logged for this engagement. The following estimates are derived from the documented scope and are labeled as such.
- Manual deduplication eliminated: The publisher described a weekly export-reimport process across ESPs, estimated at 1-2 hours per week. That's approximately 60-100 hours per year of low-value data hygiene work that is now no longer necessary.
- Compliance gap closed: Every unsubscribe that previously stayed active on 2-3 ESPs was a live CAN-SPAM exposure. The new system means one click removes the subscriber from all platforms simultaneously, with no manual follow-up required.
- Deliverability protection: Preventing continued sends to opted-out subscribers shields sender reputation across all platforms from complaint-driven degradation — the same reputation the multi-ESP setup was built to protect.
The Broader Pattern
Multi-ESP setups are common among independent publishers who have learned the hard way that platform risk is real. The problem is that each ESP treats its own unsubscribe as authoritative. There is no cross-platform standard. A subscriber who opts out of one list can keep receiving from another for months with no one catching it.
The fix is not complicated — a form, a webhook, and a handful of API calls. But it has to be built deliberately: pre-populated links to prevent wrong-address submissions, parallel branches so one ESP failure does not silently skip the others, and per-platform quirks handled (Brevo IP whitelist, Tiny Email's lookup requirement).
If your email program spans more than one sending platform and you are relying on each ESP's native unsubscribe flow to keep you compliant — you have this gap. You may not have had a complaint yet. That is not the same as being protected.
Tools Used
Fillout (form), Zapier (workflow automation), Maripost, Brevo, Tiny Email, AWeber (ESPs)
Client Profile
Solo publisher, US-based, financial newsletters. Two active lists, four ESPs.
Build This for Your Email Program
If your business sends email from more than one platform, you almost certainly have this gap. The fix is straightforward when you know how each ESP’s API handles unsubscribes — but every platform has quirks that only surface during live testing. Connex builds these integrations for email publishers, newsletters, and marketing teams who can’t afford a compliance miss.
Book a free discovery call to talk through your ESP setup. Get started here.
