Campaign Monitor: seed test your branded emails

Agencies pick Campaign Monitor for a specific reason: its multi-client architecture. You run dozens of brands from one login, each with its own list, sending domain, templates, and report dashboard. Billing rolls up cleanly. Clients see their data and nothing else. As a service delivery platform it is excellent.

The weak point shows up when a branded send goes to the wrong folder. Clients do not complain that their open rate is 18% instead of 22%. Clients complain that they forwarded a campaign to their CEO and it landed in Spam. The first deliverability problem you hear about is usually the third one that happened. By then your account health is already trending down and retention is quietly at risk.

Seed addresses are the agency-side fix. This guide covers how to structure seeds across a multi-client Campaign Monitor account, how to report placement back to clients, and which metrics to turn into SLAs.

The agency account structure

Campaign Monitor organizes by Client. Each Client has its own subscribers, segments, campaigns, and permissions. Seeds fit into this structure cleanly if you follow one rule: seeds live inside the Client, not at the agency root.

The reason is authentication. Each client sends from its own verified domain. A seed in the agency account sending to Gmail will get the wrong DKIM signature relative to the client's From-domain. You want seeds to see exactly what the client's subscribers see, which means they need to be in the Client's list and receive the mail signed by the Client's domain.

Per-client seed lists

Set up seeds inside each Client in Campaign Monitor:

1. Switch to the Client in your dashboard. Go to Lists & subscribers → Create list → name it Seed audit.
2. Generate a fresh batch of seed addresses. The free Inbox Check tool generates 20+ seed inboxes across Gmail, Outlook, Yahoo, Mail.ru, Yandex, ProtonMail, GMX, and more.
3. Import the batch as a CSV into the Seed audit list. Skip confirmation (the addresses are already validated).
4. Add custom field seed_internal=true so it is easy to exclude them from client reports.
5. Build a segment at campaign-send time: "send to primary audience + send to Seed audit list". Schedule both simultaneously.

Central placement reporting across clients

Campaign Monitor itself will not aggregate cross-client deliverability. That is where Inbox Check reports become your agency-side dashboard. Build a spreadsheet (or internal Airtable, or Notion table) that lists every Client and captures:

• Most recent send date per Client.
• Inbox placement % from the Inbox Check report (average across seed providers).
• SPF/DKIM/DMARC status at last send.
• Red flags — any seed provider where placement dropped into Spam.
• Trend vs. previous send(up/flat/down).

The operating rule for an agency deliverability manager: any client trending down across two consecutive sends gets a review. Any client under 85% placement gets a fix-it ticket opened that week. Clients above 95% placement get a monthly screenshot showing their deliverability health as part of the retainer report.

Turning placement into a client-facing metric

The best retention play for an agency is turning a commodity service (send emails for me) into a deliverability service (make sure my emails actually arrive). Seed-based placement data is how you do that.

Add a line to every client status report:

Inbox placement this month: 94%
  - Gmail: 100% inbox
  - Outlook: 95% inbox, 5% focused-other
  - Yahoo: 90% inbox
  - Mail.ru: 85% inbox
Authentication: SPF pass, DKIM pass, DMARC aligned
Compared to last month: +2%

Clients who would never open a Campaign Monitor report will read a one-line deliverability summary in a monthly email. That single line is worth the entire seed testing process. It is also a differentiator when you pitch new accounts.

Red flags to escalate immediately

Some seed-report patterns mean you have hours, not days, to act. Train the agency team to escalate on:

• DKIM failing at one provider (usually Yahoo or Mail.ru). DNS drift. Fix the record, re-seed.
• Sudden drop across all providers. Content or reputation event — check the last-sent campaign for a flagged phrase or a bad redirect.
• Spam placement at Gmail but not elsewhere. Gmail's machine-learning filter has flagged your domain. Reduce send volume, warm, and fix content flags ASAP. This one compounds fastest.
• DMARC misalignment. Client is sending from a subdomain that does not align with DKIM. Either align the signing domain or relax DMARC policy. Do not just ignore.