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How to test email marketing software suppression on four sending paths
A step-by-step suppression test for email marketing software on four paths: campaign, welcome automation, API send and synced audience, with one evidence scale and the log to keep.
What to take away
- Run the suppression test first. Mail sent to someone who opted out is the most visible failure a platform can have.
- A suppression record that stops campaigns but not API sends is a partial result. Write it down as partial.
- Score every result on one scaleproven, partial, absent, unknown or planned.
- Vendor documentation shows intent. Only a test in your own account shows behavior.
Vendor pages from Brevo, Kit, Mailchimp and MailerLite describe capability in broad terms. That is the start of a shortlist, not evidence. This article gives one test, suppression on four sending paths, and the steps to run it in your own account. Transactional email, SMS, RSS-to-email, imports and manual admin removals are outside this test. Run the same method on any of them that your business uses.
Why suppression comes first
The FTC's CAN-SPAM compliance guide covers the commercial email rules for United States senders. A working opt-out must be honored within 10 business days, and a platform that keeps sending to an opted-out address after that window puts the sender at risk.
Canada's Anti-Spam Legislation requires consent for commercial email to Canadian recipients. The CASL journey rules cover consent records. Test those records along with the opt-out, because a platform can honor an unsubscribe and still lose the consent trail.
Central suppression matters most when one contact sits in several systems. A contact can be unsubscribed in the email tool and still be in a synced audience, a welcome automation or an API integration. Each of those paths is a separate test.
What the vendors document
The table lists what each vendor documents, and what its public material says about the behavior this test checks. Check each entry against the vendor's current documentation before you rely on it. A "not documented" entry is a question to put to the vendor and a point to test in your own account.
Four behaviors
What the vendor documents
- Brevo
- Campaigns, transactional email and SMS share one contact database; contact and list APIs are documented.
- Kit
- Automations trigger from subscriber tags and form events; tag-based sequencing is documented.
- Mailchimp
- A published compliance policy requires permission before a send; sending limits bind to the plan tier.
- MailerLite
- Pricing bands by subscriber count; the automation builder supports conditions, delays and goal steps.
Public evidence on behavior
- Brevo
- Suppression coverage across a synchronized CRM audience is not documented.
- Kit
- Rollback of a running sequence is not documented.
- Mailchimp
- Suppression behavior across synchronized audiences is not documented.
- MailerLite
- Partial-failure and retry handling are not documented.
The rollback and partial-failure rows are outside this test. The suppression row for Brevo and Mailchimp is the one to check first.
One scale for every result
Use one scale for every result: proven, partial, absent, unknown or planned. Proven means you ran the test yourself and kept the log. Partial means some paths behaved and others did not. Planned means nothing exists yet, and a planned feature cannot satisfy a mandatory requirement.
Write the path names into the result. "Partial" with no detail tells the next reader nothing about which send went out.
The suppression test, step by step
Suppression script
- Create two test contacts, subscribe both to two lists, then unsubscribe one from the second list only.
- Trigger four paths to that contacta campaign, a welcome automation, an API send and a synced audience.
- Wait one full send window and count what reached a real inbox, not a preview pane.
- Export the suppression log and match contact IDs, paths and timestamps.
- Resubscribe, resuppress and repeat once, to catch cached or delayed states.
- Record the outcome on the evidence scale and note who owns the re-test.
Score the result by path. For example, if a campaign and a welcome automation are blocked but the API send reaches the inbox, the result is partial, and the note should name the API path. Do not average the paths into one score.
Record the hours
Record how long each step takes your own team, because setup time varies with the platform and the staff involved. Add that total to the buying case, along with the hours to re-run the test each month.
Keep the export and the log with the score. A reviewer who cannot see the raw evidence has to take the result on trust, and that is the same as having no result. The export is the record that shows when each opt-out was honored, which is what the CAN-SPAM 10-business-day rule measures.
