By separating at four levels, so one client's mistake cannot reach another client's domains: domains per client and never shared, tenants or workspaces per client where the provider allows it, tracking subdomains per client because link reputation travels with the link, and separate sending IPs if you self-host. Everything else, the reporting, the white-label branding, the billing, sits on top of that separation and is easier than it.
Published by emailcampaign.ai, which sells agency infrastructure. The per-client costs quoted here were read from each vendor's own pricing pages on 19 September 2026.
The risk that only agencies carry
A client hands you a list they bought. It bounces at eight percent. If that client's mailboxes sit in a tenant shared with three other clients, or send through a tracking domain shared across the book, or share a self-hosted IP with everyone else, the damage does not stop at their account. Their bad month becomes your bad quarter, across clients who did nothing wrong and will still see fewer replies.
This is why separation is the first decision and the branding is the second.
Sizing the fleet per client
Divide each client's daily target by sixteen to twenty, which is what one domain carries at two mailboxes and eight to ten sends each. A client who wants two hundred cold emails a day needs about twenty mailboxes on ten domains. Multiply across the book: five such clients is a hundred mailboxes on fifty domains, and fifty domains means fifty sets of DNS records to write, verify and keep correct.
The four levels of white-label, which are not the same thing
Vendors use one word for four products. A logo on a dashboard. A client portal on your own domain where the client reads reports. A per-client workspace, where campaigns and data are separated. And a client door on the client's own domain, where their staff sign in to their own mailboxes and their administrator controls privacy and forwarding.
Pick by what the client will actually do. If they read a monthly report, a portal is enough and the cheapest option wins. If their sales people answer replies themselves, they need somewhere to answer them, and a reporting portal will not survive that conversation.
What it costs per client
| Vendor | Software | Per client | Mailboxes |
|---|---|---|---|
| Smartlead | $32.50 a month | $29 a client workspace | Partner-supplied, about $4.50 a mailbox plus $13 a domain |
| Instantly | $37.60 a month | Branded portal from the $77.60 plan | Pre-warmed Google accounts $10 each, Instantly keeps the domains |
| Saleshandy | $34 a month | White-label from the $149 plan, no per-client fee stated | $2.99 to $3.99 a mailbox |
| Woodpecker | $35 a month | $5 a client plus a $27 agency panel | $6 a Google or Microsoft address; bought domains stay inside Woodpecker |
| emailcampaign.ai | $39 or $94 a month | Client door included | Provider seat price plus a $5 setup, in the client's own name |
Questions to settle before the first send
Who owns the domains? Some vendors keep ownership of what they provision, and some bought domains cannot be used outside the vendor at all. Get it in writing.
Can one client see another? Ask specifically about a client with campaign access rather than the default view, and test it with two dummy clients. At least one major vendor documents that a client with campaign access sees every campaign in the workspace.
What happens at offboarding? Domains, mailboxes, mail history, the client list. If the answer is a support ticket, that is your answer.
How long is onboarding, honestly? Three weeks from signature to full speed, and almost all of it is warm-up. Clients accept that timeline when it is explained at the start and never when it is explained in week two.
Questions, answered straight
- How many inboxes does a cold email agency need?
- Per client, the daily target divided by sixteen to twenty. Across a book of thirty to forty clients sending a few hundred a day each, that reaches several hundred mailboxes, which is the point where the operational work has to be automated or staffed.
- Should the agency or the client own the domains?
- Decide it in writing before the first send. Client ownership is cleanest and is what we default to. Agency ownership is workable if the contract says what happens at the end. The failure mode is discovering the answer during an offboarding.
- What belongs in the monthly client report?
- Sends, replies, positive replies and meetings by client and mailbox, plus the deliverability line: bounce rate, complaint rate and any provider-level refusals. The last is the leading indicator, so raise it before the client notices fewer replies.
- Can I promise results in week one?
- Not honestly. Week one is domains, mailboxes, DNS, list and copy. Weeks two and three are warm-up. Week four is full volume. Anyone promising week-one volume is sending from mailboxes carrying a stranger's history, or sending too much too early on the client's domain.
Published 19 September 2026. Updated 19 September 2026. Written by the team that runs the infrastructure; numbers come from the platform's own provisioning and sending, and from the providers' published documentation at the time of writing.