The four layers, and the fifth everyone forgets
- Domains. Lookalikes of your brand, registered in your name, each forwarding its root to your real site. One sending mailbox per domain is the safe default; two or three per domain once a domain has a month of clean history.
- Mailboxes. At Google Workspace, at Microsoft 365, or on a server of your own. Real names, real people, one seat each.
- Authentication. SPF, DKIM with a 2048-bit key, DMARC that starts at monitoring and moves to quarantine once the reports are clean, plus the provider's postmaster verification. Written correctly the first time and re-checked continuously, because DNS drifts.
- Warm-up. Two to three weeks of rising, replied-to traffic that gives each new mailbox a history before it writes to a stranger, then a maintenance level for the life of the mailbox.
- Monitoring that acts. Placement tests at Gmail and Outlook, bounce and refusal classification per provider, DMARC report reading, and automatic pauses. Infrastructure without this layer works until the day it silently does not.
How much you need for a daily volume
The one number to internalise: 8 to 10 cold emails per mailbox per day after warm-up, with 5 to 15 as the hard band. Volume is a fleet-size question, not a per-mailbox one.
| Cold emails per day | Sending mailboxes | Domains (one mailbox each) | Rough monthly cost on Google Workspace |
|---|---|---|---|
| 50 | 5 to 7 | 5 to 7 | $42 to $59 in seats, plus $7 a month in domains |
| 100 | 10 to 13 | 10 to 13 | $84 to $109 in seats, plus $13 a month in domains |
| 500 | 50 to 63 | 50 to 63 | $420 to $529 in seats, plus $63 a month in domains |
| 1,000 | 100 to 125 | 100 to 125 | $840 to $1,050 in seats, plus $125 a month in domains |
| 5,000 | about 500 | about 250 with two mailboxes each | $4,200 in seats, plus $250 a month in domains |
Seat prices are Google's flexible rate of $8.40 a user a month billed through the platform; domains are about $12 a year each; setup is $5 one-time per mailbox. Microsoft 365 seats are at Microsoft's rate. Self-hosted servers start at $39 a month, or three for $99, and carry many mailboxes each. The calculator prices any volume to the cent with one, two or three mailboxes per domain.
What one approval does
You choose a volume and a provider mix; the platform shows the fleet and its price; you approve once. Then, without another click from you:
- It buys the domains through the registrar and puts them in your name, at the registrar's daily pace, and points each root at your website.
- It creates the mailboxes: a Workspace customer and users, or a Microsoft 365 tenant and users, or accounts on a dedicated mail server it stands up for you.
- It writes the DNS: MX, SPF, DKIM (reading the selectors the provider actually assigned rather than guessing them), DMARC and the postmaster record, each shown in the DNS console before it goes live, with the authentication records requiring an explicit confirmation.
- It keeps the credentials in a vault and connects each mailbox with an application credential; no password is typed anywhere, and every use is audited.
- It starts the warm-up on every mailbox at the provider's floor and steps it up daily, threading real replies, keeping every warm-up message out of your working inbox, and dropping to a maintenance level when the ramp ends.
- It caps sending per mailbox, ships with tracking off, and applies the same discipline whether the mailbox is Google, Microsoft or self-hosted.
If a step fails, the step retries and the console says so; nothing is recorded as done that was not done. That last sentence is the one most tools cannot make.
Deliverability as an operating system, not a dashboard
- Refusals are read correctly. A 5.7.x refusal is a provider's verdict about the sender, not the recipient. The platform pauses that sender for that provider and keeps the recipient; suppressing the recipient would hide the real problem.
- Placement is measured, not assumed. A test sends from each mailbox to seed inboxes at Gmail and Outlook and reports inbox or spam per provider.
- DMARC reports are read for you. A dedicated mailbox receives them and the console shows when something outside your fleet starts sending as your domain.
- Replies are attributed. The unified inbox counts a reply only when it answers one of your sends, and out-of-office messages are not replies.
- Burned domains are replaced, not mourned. Pause, buy, set up, warm, resume, while the rest of the fleet keeps sending.
Self-hosted, when it makes sense
Provider mailboxes are the fastest route to the inbox. Self-hosted servers make sense when the fleet is large, when you want reputation you own rather than rent, or when a provider has already made up its mind about you. The platform stands up dedicated servers with their own IPs, creates mailboxes on them, writes the same authentication, warms them more slowly because a fresh IP needs it, and monitors their reputation. Capacity per server is set by the operator and shown in the console; a full server never silently caps your fleet.
Questions, answered straight
- What counts as cold email infrastructure?
- Everything a message needs before the words matter: domains that are not your primary one, mailboxes on those domains at a provider or on your own server, authentication records that pass (SPF, DKIM, DMARC), a warm-up period that gives each mailbox a history, and the monitoring that tells you when any of it starts to slip.
- Why not just add more mailboxes to my company's Google Workspace?
- Because a cold email reputation problem would then hit the domain your customers, invoices and password resets depend on. Cold sending lives on secondary domains in separate accounts, so a burned domain costs you one domain and nothing else.
- Provider mailboxes or self-hosted?
- Provider mailboxes (Google Workspace, Microsoft 365) inherit the provider's reputation and place well quickly; you pay a seat per mailbox. Self-hosted servers give you IPs and a reputation you own, cost less per mailbox at scale, and take longer to warm. Many fleets run both; the platform provisions and warms either.
- How long from approval to sending?
- Domains, mailboxes and DNS are the same day. Warm-up to full volume takes two to three weeks. Budget three weeks from purchase to full-speed campaigns.
- What if a domain gets burned?
- It happens, and the fleet is designed for it. A domain whose placement slips is paused, its mailboxes stop sending, and a replacement domain is bought, set up and warmed while the rest of the fleet continues. Nothing you send from is your primary domain, so nothing else is affected.
- Can I bring domains and mailboxes I already have?
- Yes. Existing mailboxes connect with app passwords or OAuth, DNS you host elsewhere can be checked and corrected, and warm-up can start on mailboxes you did not buy here.
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.