The best cold email infrastructure tools are the mailbox providers that buy your sending domains, set up SPF, DKIM and DMARC, create the inboxes and warm them up, separately from the sequencer that sends your campaigns. Pick by mailbox type (Google, Microsoft or private IP), how the bill is counted and whether you want the setup done for you or a dashboard to run yourself.
Why would anyone pay a separate company to run their mailboxes when Google Workspace and Microsoft 365 will sell you a seat in five minutes? Because outbound at any scale means dozens of domains and many more inboxes, each one needing DNS records, warm-up and a link into your sequencer, and doing that by hand is where weeks disappear and deliverability goes wrong.
This layer sits underneath your campaign tool. Your sequencer decides who gets which email and when; the infrastructure decides whether that email arrives from a well-configured, warmed-up mailbox on a domain that isn't your main company address. Get the second part wrong and the best copy in the world lands in spam.
Mistakes that cost outbound teams their domains
- Sending cold email from your main company domain because it was quicker. When it gets flagged, invoices and support replies suffer too.
- Buying every inbox from one mailbox type. Spreading across Google and Microsoft gives you a fallback if one starts filtering your mail harder.
- Skipping warm-up to hit a launch date. A few weeks saved at the start often means months of poor placement later.
- Comparing headline mailbox prices without checking slots, tenants, minimums or per-send charges.
- Treating infrastructure as a one-off job. Domains age and reputations drift, so someone needs to own monitoring every week.
Ten providers to put on the shortlist
Mailforge
Distributed cold email mailboxes and domains with DNS records set up automatically, for outbound teams who want capacity spread wide without registrar chores.
Infraforge
If shared IPs make you nervous, this one builds private cold email infrastructure on dedicated IPs instead.
Maildoso
Outbound mailboxes sold in volume bundles, with self-healing and IP rotation aimed at keeping cold sends out of spam.
Inboxkit
US-IP Google and Microsoft mailboxes, DNS configured automatically, plus an MCP server you can plug into your own tooling.
Zapmail
A Google Workspace specialist for cold email, offering pre-warmed mailboxes and a deliverability test before your first campaign goes out.
Premium Inboxes
Agencies that would rather hand the whole job over get official Google Workspace and Microsoft 365 inboxes built for them, warm-up already switched on.
Mission Inbox
Sits underneath the sequencer you already use, running outbound sending on dedicated IPs rather than replacing your campaign tool.
Mailreef
Mailboxes on a dedicated server you control, pitched at experienced cold emailers, teams and agencies.
Hypertide
Automates cold email infrastructure across Google inboxes and Microsoft Entra, so a new batch of domains goes live without manual DNS work.
Primeforge
When the plan is to split sending between Google and Microsoft from day one, this supplier sells both mailbox types for cold outreach.
Four forks to settle before you buy a single mailbox
Domains. You'll want sending domains that sit apart from your main one, so a burnt domain never touches your company email. Some providers buy and configure the domains for you as part of the order; others expect you to bring your own and point the records at them. Ask who owns the domain at the registrar, because that decides what happens if you ever leave.
Mailboxes. This is the biggest fork. Google Workspace and Microsoft 365 inboxes look like any ordinary business mailbox to the receiving server. Private-IP setups put you on dedicated sending infrastructure that you don't share with anyone, which removes noisy neighbours but makes the reputation of those IPs your problem alone. Several providers here sell both Google and Microsoft side by side, so you can split volume across the two.
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Warm-up. New inboxes need a quiet period of gentle, positive activity before they carry real campaigns. One provider here switches warm-up on during setup and another offers pre-warmed inboxes; with others you may be adding it yourself. If yours doesn't include it, our guide to email warm-up tools covers that piece.
Hosting and setup. At one end, a managed service does the domains, DNS, inbox creation, sequencer connection and warm-up for you and talks to you in a shared Slack channel. At the other, you get a dashboard or an API and do the clicking yourself. An agency spinning up client after client will get more from the API; a sales team launching once will get more from the hand-holding.
The main types at a glance
| Type of provider | What you're buying | How the bill is counted | Examples here |
|---|---|---|---|
| Google and Microsoft mailbox providers | Workspace or 365 inboxes with DNS set up for cold sending | Per mailbox, sometimes per Microsoft tenant or per domain | Inboxkit, Hypertide, Primeforge |
| Google Workspace specialists | Workspace inboxes with pre-warmed options and checks | A plan with a set number of mailboxes | Zapmail |
| Private or dedicated infrastructure | Your own IPs or server under your sequencer | Per mailbox, or a monthly plan, sometimes plus a per-send charge | Infraforge, Mission Inbox, Mailreef |
| Distributed mailboxes | Many mailboxes spread across many domains, DNS set automatically | Per mailbox slot, with a minimum number of slots | Mailforge |
| Volume bundles with rotation | Outbound mailboxes with self-healing and IP rotation, sold in bundles | Per mailbox, the rate falling as the bundle grows | Maildoso |
| Done-for-you setup | Domains, DNS, inboxes, warm-up and sequencer hook-up handled for you | Per inbox, priced in bands by volume | Premium Inboxes |
What I'd choose in your position
If you're an in-house sales team running one product, a done-for-you provider on Google Workspace and Microsoft 365 is the calm choice: the setup becomes someone else's job and you get on with selling. If you're an agency adding clients every month, favour a provider with an API or a fast self-serve dashboard and per-mailbox billing with no minimums, because you'll be creating and retiring domains constantly.
If your volume is high and you're confident managing reputation, look at the private-IP and dedicated-server providers, and accept that nobody else's good behaviour will carry you. And if you haven't settled on a campaign tool yet, sort that first with our guide to cold email software; the infrastructure should fit the sequencer, not the other way round.
How the bill is counted
Pricing in this category looks simple and isn't, because providers count different things. Per-mailbox pricing is the norm, but even that splits. Some charge one flat rate for each mailbox with no plans or included slots. Others size the price on mailbox slots rather than active mailboxes, so you pay for capacity you've reserved whether or not every inbox is live. Some sell volume tiers where the per-mailbox rate falls as the bundle grows, and at least one states a daily sending cap for each mailbox, which matters more than the price if you were planning to push volume.
Microsoft can be billed differently again: by tenant, with a ceiling on how many mailboxes each tenant holds. One provider here also prices its Microsoft Entra option by domain with a set number of inboxes included, while its Google inboxes are counted one by one. At the dedicated end, two providers here sell a monthly plan with mailboxes included rather than a per-mailbox rate, and one of them adds a small charge for every send and a twelve-month commitment.
Then there are domains. Some providers add a yearly charge for each domain, taken up front with the order; others leave domains to you. When you compare two quotes, convert both to the same unit: total monthly cost for the number of sending inboxes you'll run, including domains, warm-up and anything charged per send. Annual billing can lower the rate, so check whether the number you're looking at assumes it. One of the ten, Primeforge, didn't show a price in what was checked for this guide, so you'd need to ask.
For a rough budget: on the vendors' own pricing pages this month, the seven providers here that quote a rate per mailbox mostly sit at about $2.50 to $4 a mailbox a month at small-team sizes, a little higher for insured or pre-warmed mailboxes, before domains, and bundle pricing can drop well below that as volume grows. The plan-based providers and any per-send charge sit outside that range, so price them on your own inbox count.
Rehearse with one domain before you scale
Before you order fifty inboxes from anyone, run a small rehearsal that shows how the provider behaves end to end. It takes a couple of weeks of calendar time but very little effort.
- Order one sending domain and three inboxes, and time how long it takes from payment to working mailboxes.
- Check the DNS yourself rather than trusting the dashboard: SPF, DKIM and DMARC should all be present and passing on a test email you send to your own Gmail and Outlook addresses, using the show-original view.
- Connect the three inboxes to the sequencer you already use and note anything you had to fix by hand.
- Let warm-up run, then send a small batch to seed addresses you control on Google and Microsoft and record where each one lands.
- Ask support one awkward question, such as how you'd move these domains out if you left, and judge the answer and the reply time.
If any step needed a ticket or a workaround, multiply that by fifty before you decide. Our guide to email deliverability tools covers the testing side if you want more than a seed check.
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