Cold Email Agencies: How to Run Infrastructure per Client

A cold email agency needs four things from its infrastructure: one workspace per client with its own domains and mailboxes, a volume plan for every client and for the whole book, a way to hand the mailboxes to the sequencer each client runs on, and an API to repeat the onboarding. On Outreach2day, workspaces and team members are free, each mailbox is $2.50 a month with warmup and a sequencer included, mailboxes sync to Instantly and Smartlead with an API key, and the REST API and the MCP server (OAuth sign-in) cover the per-client steps. Plan three weeks from the first order to full volume for every new client.

We make Outreach2day; the numbers below are ours where a vendor is needed, and the steps apply to any stack. For the layers themselves, start with how to set up cold email infrastructure; to compare vendors, see best cold email infrastructure providers.

Why Agencies Separate Every Client

Receiving providers judge a sender by its domain. Google's sender guidelines say Gmail "tracks volume, feedback, and limits per domain and IP address" and that "DKIM and SPF quotas are specific to your domain." If two clients send from the same domain, the client with the weaker list sets the reputation for both.

Separate per client:

• Domains. No domain sends for two clients. A client's domains carry only that client's campaigns.

• Mailboxes. Mailboxes sit on their client's domains, up to 5 per domain. See mailboxes per domain.

• Workspace. One workspace per client keeps domains, mailboxes, reply threads and analytics apart, so reports and offboarding touch one client only.

Domain separation does not isolate the sending IPs. Google's same page says "The activity of any senders using a shared IP address affects the reputation of all senders for that shared IP address." When one client's results drop, check whether other clients on the same IPs dropped too before you blame the domain. The burned domain answer walks through that test.

Who Owns the Domains: Client or Agency

Decide this before the first purchase. It sets who pays for renewals and what happens when the client leaves.

In Outreach2day, domains bought in the app are registered for one year with the registrant contact details you enter. Enter the client's details if the client should own them. The domains belong to the registrant, and support moves them to the owner's own Namecheap account on request. Domains a client already owns connect by pointing their nameservers to ours; the change takes 24 to 48 hours.

Renewal is not automatic. A domain that expires stops its mailboxes, so put renewal dates for every client in your own calendar.

Size Each Client Before You Buy

Work backwards from the client's daily cold volume:

1. Mailboxes = cold emails per day ÷ 25 (up to 25 cold emails per mailbox a day, excluding warmup).

2. Domains = mailboxes ÷ 5 (up to 5 mailboxes per domain).

3. Round both up. Add a spare domain or two for replacements.

The cold email capacity calculator does the arithmetic for any volume.

Plan Volume Across All Clients

Size the whole book of clients at once. Example: an agency with eight clients, two small, four medium and two large.

At $2.50 per mailbox that is $460 a month for 184 mailboxes, with warmup and a sequencer included, plus 38 domains at $13 a year each as .com ($494 a year). $2.50 is the list price; volume discounts are available for large orders through sales.

Three rules for the plan:

• Keep warm spares. A new mailbox needs about 21 days to reach full volume. Keep a spare domain or two per client warming, so a burned domain is replaced the same day.

• Reuse slots. Billing is per mailbox slot. When a domain burns, delete its mailboxes and create new ones on a fresh domain in the same slots; only the new domain costs extra.

• Stagger new clients. Two clients signed in the same week both spend three weeks in warmup. Start their domains on different days so a problem shows on one first.

Cost per Client at Three Sizes

Outreach2day charges $2.50 per mailbox a month (list price), with warmup, the sequencer, the reply inbox and per-mailbox analytics included. Domains are $13 a year for a .com and $5 for a .info. A card processing fee (2.9% + $0.30) is added at checkout, on new domains and the first month of mailboxes. The minimum order is 12 mailboxes ($30 a month).

The arithmetic: 300 ÷ 25 = 12 mailboxes, 12 ÷ 5 = 2.4, rounded up to 3 domains; 12 × $2.50 = $30 a month, 3 × $13 = $39 a year, 12 × $30 + $39 = $399. The same method gives the other rows. Card fees and spare domains are not included. With .info domains the domain column drops to $15, $20 and $40.

The client pays for about three weeks of warmup before full volume. Put that in the proposal so the first invoice is not a surprise.

How to Onboard a New Client

Run the same steps for every client. The timeline assumes you order on day 1.

1. Agree the daily volume. Take the client's target meetings, their past emails-per-meeting if they have it, and turn it into a daily cold volume. Size mailboxes and domains from it as above.

2. Create a workspace for the client. One workspace per client. Name it after the client so reports and invoices match.

3. Buy or connect the domains. Buy new domains with the registrant details you agreed, or connect the client's own by pointing nameservers. Use variations of the client's brand; see domains for cold email for naming and extensions. Never send from the client's main domain (why).

4. Create the mailboxes. Up to 5 per domain, with real sender names from the client's team. New mailboxes are ready within 24 hours. SPF, DKIM, DMARC and the redirect to the client's website are set up for you.

5. Start warmup and wait 14 days. Each mailbox sends 25+ warmup emails a day to Google recipients, 25 to Outlook and 25 to other providers. Send no cold email in this period.

6. Ramp to full volume by day 21. Start low cold volume from day 14, raise it over the following week, and reach up to 25 cold emails per mailbox a day around day 21. Keep warmup running while you send.

7. Connect the sending tool. Send from the included sequencer, or connect the client's Instantly or Smartlead account with an API key so the mailboxes are added there (next section). Other tools take a CSV export or the SMTP/IMAP logins. Load the client's copy and a follow-up sequence; keep links out of the copy.

8. Set the reporting cadence. Agree which numbers the client sees and how often, before the first send (next section).

Sync Mailboxes to Instantly or Smartlead per Client

Many agencies sell campaigns run in Instantly or Smartlead and buy the mailboxes elsewhere. The pattern per client:

1. Create the client's workspace and mailboxes in Outreach2day.

2. In that workspace, connect the client's Instantly or Smartlead account with its API key. We add the mailboxes to that account.

3. Warmup keeps running on our side. The sequencer sends and reads replies over SMTP and IMAP.

4. When the client leaves, disconnect the workspace; the other clients' connections are untouched.

The mailbox line changes, the sequencer plan does not. At 20 mailboxes a client, our mailboxes cost $50 a month against $100 for 20 Instantly done-for-you Google accounts at $5 and $90 for 20 Smartlead SmartSenders at $4.50 (Instantly pricing, Smartlead pricing, checked September 29, 2026). Instantly also says "Each workspace requires its own subscription" (Instantly billing), so an agency with a workspace per client there pays a plan per client; our workspaces are free. Done-for-you accounts from either sequencer stay inside it, so moving a client to another tool means new mailboxes; ours move by API key or CSV. Step by step: mailboxes for Instantly and Smartlead.

Reporting to Clients

Report per client, split by recipient provider, because mail from the same mailbox can land in the inbox at Outlook and in spam at Gmail. Outreach2day shows these per mailbox, and each workspace holds one client's numbers:

• Warmup inbox, spam and bounce rate.

• Sends by recipient provider: Google Workspace, Microsoft 365, other.

• Replies sorted by type, from one inbox for all the client's mailboxes.

• Google and Outlook placement tests.

Show reply counts next to sends, and flag any mailbox or domain whose warmup inbox rate falls. A placement test is a sample of seed inboxes, so report it as a trend across tests. Inbox placement is measured and has no guarantee, so don't promise it to the client either.

Billing Across Clients

• Workspaces and team members are free. There is no platform fee and no per-seat charge; you pay for mailboxes and domains.

• Each workspace has its own first order. Mailboxes are ordered in the app per workspace, and the card saved on a workspace pays for its later domain purchases.

• Changes are prorated one way. Mailboxes you add are charged right away, prorated; mailboxes you remove give no credit for the current month.

• Large orders. $2.50 is the list price. Volume discounts are available for large orders: book a call or contact sales. See pricing.

Billing is monthly by card, month to month, with no contract. That matches client retainers that can end at a month's notice.

Automate Onboarding With the REST API

Every account has a REST API (docs at dev.outreach2day.com; 10 requests a second, 300 a minute, 1,000 an hour and 10,000 a day). For an agency the useful calls are the ones you repeat per client:

Three limits matter. A workspace created over the API has no card yet, so domain purchases in it return 402 until its first order is made in the app. Mailboxes are ordered in the app. And a purchase call is the purchase: there is no confirm step and no idempotency key, so never retry a purchase that timed out before checking GET /domains. Request bodies and error codes are in the cold email API overview and how to buy domains via API.

White Label and Client Access

White-label cold email usually means a client portal under the agency's brand. Some sequencers offer it: Instantly's agency white-labeling page says it "offers a white-label solution for agencies on Hyper Growth and Light Speed plans," lets you share "Campaigns(View or Edit), Unibox, Analytics, CRM, and Blocklist" with clients, and puts the client login on your own subdomain with your logo. The same page says "you can only configure one agency portal per workspace."

Outreach2day does not offer a white-label portal. If you want clients to log in under your brand, run the campaigns in a sequencer that offers one and use Outreach2day for the mailboxes, connected with an API key.

Agency Cold Email Tools by Layer

We make Outreach2day, so it is listed first; the other entries use each vendor's own public pages. For ten mailbox providers side by side, with the monthly cost at 25, 100 and 400 mailboxes, see cold email infrastructure tools compared by price.

Offboarding a Client

When a client leaves, settle the domains first, then cancel.

1. Export what you need. Reply threads live in the client's workspace; save what the contract says the client gets.

2. Hand over the domains. Domains registered in the client's name are theirs. Support moves them to the client's own Namecheap account on request. DNS records and the redirect do not follow the domain: the client sets them up again at the new home.

3. Cancel the client's mailboxes. Cancel through the in-app chat or support@outreach2day.com. Cancelling deletes the mailboxes and they cannot be restored, so the client cannot keep sending from those addresses through us. There are no charges after the current paid month.

4. Tell the client about warmup. If they send from the same domains with a new provider, the new mailboxes need warmup again.

Set it up from your AI assistant. Add this URL to Claude, ChatGPT, Cursor, VS Code or another MCP client and sign in with your Outreach2day account when it asks:

https://public.outreach2day.com/mcp

To add it to every MCP client on your computer at once, run the installer:

curl -fsSL https://outreach2day.com/install | sh

For a new client, the assistant checks domains and quotes mailboxes; you approve the quote and pay on Stripe; it sets up DNS, warmup and campaigns in that client's workspace. Setup per assistant: Outreach2day MCP.

FAQ

What infrastructure do cold email agencies use?

Separate sending domains and mailboxes per client, warmup, a sequencer and a reply inbox. Some agencies buy Google Workspace or Microsoft 365 accounts from a reseller and send from Instantly or Smartlead; others use SMTP/IMAP mailboxes with warmup and a sequencer included, as Outreach2day sells them at $2.50 a mailbox. Vendors compared: best cold email infrastructure providers.

Are workspaces and team members free?

Yes, on Outreach2day. There is no platform fee and no per-seat charge; you pay for mailboxes ($2.50 each a month, from 12) and domains ($13 a year for a .com, $5 for a .info). See pricing.

How many mailboxes does an agency need?

Add up the daily cold volume of every client, divide by 25 and round up per client, then add spares. Eight clients sending 4,600 cold emails a day between them need 184 mailboxes on 38 domains.

Can I use the same mailboxes for two clients?

No. Mailboxes on one domain share its reputation, so one client's complaints would lower the other client's placement. Give each client its own domains and mailboxes.

How long does it take to onboard a new cold email client?

About three weeks to full volume: mailboxes are ready within 24 hours, warmup runs alone for 14 days, low cold volume starts on day 14 and full volume comes around day 21.

How much does cold email infrastructure cost per client?

At Outreach2day, a client sending 500 cold emails a day needs 20 mailboxes ($50 a month) on 4 domains ($52 a year as .com), plus a card processing fee (2.9% + $0.30) at checkout on the domains and the first month. The sequencer and warmup are included.

Should the agency or the client pay for domains?

Either works if the registrant is agreed in writing. Registering domains in the client's name makes the handover simple when the contract ends.

Do I need Google Workspace accounts for client campaigns?

No. Outreach2day mailboxes are standard SMTP/IMAP mailboxes (no Google Workspace or Microsoft 365 seats), and they work with any sending tool that accepts SMTP/IMAP.

Sources

Checked September 2026:

• Google: Email sender guidelines: Gmail tracks volume, feedback and limits per domain and IP address; DKIM and SPF quotas are per domain; shared IP activity affects all senders on that IP.

• Instantly: Agency white-labeling: white-label solution on Hyper Growth and Light Speed plans; shared sections (Campaigns, Unibox, Analytics, CRM, Blocklist); client login on your subdomain with your logo; one agency portal per workspace.

Create one workspace per client and size the first one with the numbers above.