Seed testing your Brevo campaigns

Brevo (rebranded from Sendinblue in 2023) is popular because its pricing is metered on emails rather than contacts, and because marketing and transactional share one account. That sharing is also the platform's biggest deliverability risk: marketing and transactional streams sit on the same sending IPs and share reputation. If your transactional flow breaks — a new payment confirmation email with a flagged link, a password reset with a shady image host — your newsletter placement drops with it. Seed tests are the only fast way to see this drift.

Step 1 — Create a Brevo contact list for seeds

1. In Brevo, go to Contacts → Lists → Add a new list.
2. Name the list Seed panel. Leave it assigned to your main folder so you can find it easily.
3. Import your seed addresses. Inbox Check will give you 20+ fresh addresses per test across Gmail, Outlook, Yahoo, Mail.ru, Yandex, ProtonMail and GMX. Paste them into the Brevo import form and mark them as subscribed.
4. Add an attribute called IS_SEED (boolean) and set it to true for every contact in this list. You can use this attribute later to exclude seeds from reporting.

Brevo's contact quota is not charged per contact — you pay per email sent — so the seed list itself is free to maintain. The only cost is the 20 or so emails per campaign that go to the seeds.

Step 2 — Include seeds in campaigns

When you create a campaign in Brevo, the recipient picker lets you select multiple lists. Pick your main list AND the Seed panel list in the same campaign. Brevo sends one message per unique email, so if a seed is somehow also in your main list (shouldn't be, but can happen) you won't double-send.

If you prefer to run seeds through a separate campaign for audit cleanliness — same content, same time, two sends — use the Duplicate Campaign feature. Pick Seed panel as recipient, hit Send Now immediately after the main send launches.

Automations

For Brevo automations (welcome series, abandoned cart), add the Seed panel as an entry point so seeds trigger the automation like real users. You can also manually enrol a seed contact into an automation from the contact detail view to dry-run the entire flow.

Step 3 — Seed transactional email via the API

Transactional is where Brevo senders most often miss reputation drift. The API-driven flow never runs through the campaign UI, so seeds aren't automatically included.

The cleanest pattern is to add a permanent BCC or CC to your transactional template for one or two seed addresses, or wire your send-email API call to CC a rotating seed:

POST https://api.brevo.com/v3/smtp/email
Headers: api-key: xkeysib-...

{
  "sender": { "email": "noreply@yourdomain.com", "name": "Your App" },
  "to":   [ { "email": "customer@example.com" } ],
  "bcc":  [ { "email": "seed-transactional@yourseedpanel.io" } ],
  "subject": "Order #{{ order_id }} confirmed",
  "htmlContent": "..."
}

One transactional seed BCC on every order confirmation is enough to catch a reputation drop in the morning instead of three days later. Rotate the seed address weekly so you don't burn the same mailbox.

Step 4 — Read the placement map

After each send, log into the Inbox Check test (or your seed tool of choice) and read the map. A typical healthy Brevo result looks like this:

Gmail:       3/3 inbox
Outlook:     2/2 inbox
Yahoo:       2/2 inbox
Mail.ru:     2/2 inbox
Yandex:      2/2 inbox
iCloud:      1/1 inbox
ProtonMail:  1/1 inbox
GMX:         1/1 inbox

Overall: 100% Inbox — clean send
SPF: pass · DKIM: pass · DMARC: pass

An unhealthy Brevo result — one that should make you pause the next campaign — looks different. Typically you'll see all other providers OK and one of Gmail/Outlook drop several messages at once. Gmail drops usually mean engagement reputation; Outlook drops usually mean either SNDS reputation or a SmartScreen content trigger. Brevo support can rebalance your IP pool if the drop is pool-wide, but they need you to show evidence, and seed results are the strongest evidence you can bring.

Step 5 — Shared IP pool nuances

Brevo's lower tiers share IP pools across many customers. That means your reputation is a weighted blend of your behaviour and your neighbours' behaviour. Three things follow:

• Your placement can drop without you changing anything. A noisy neighbour on the same pool can drag Outlook and Yahoo reputation down for a day. Seed tests catch this within minutes.
• Pool drift is most visible on Outlook. Outlook weights IP reputation heavily; Gmail weights domain reputation more. If you see Outlook dropping while Gmail stays clean, suspect pool.
• Dedicated IP is not always the fix. A dedicated IP only helps if your volume is high enough to maintain reputation on it — usually 100k+ sends per month. Below that, you'll warm it forever and never reach parity with the shared pool.

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