Best cold email infrastructure providers (2026 buyer's guide)
Updated 17 October 2026 · 8 min read
Short answer
The best cold email infrastructure provider is the one that sells the mailbox type you want (real Google or Microsoft seats, the provider's own SMTP, or Microsoft tenants), lets you own your domains, automates DNS and warmup, and fits your volume and billing needs. For Google Workspace mailboxes at a low monthly price, ReplyDak, Inboxkit and Zapmail lead; for Microsoft 365 today, Zapmail, Inboxkit and Primeforge; for the lowest cost at very high volume, own-infrastructure providers such as Maildoso.
What cold email infrastructure includes
Cold email infrastructure is the sending layer under your sequencer: separate domains, mailboxes on those domains, DNS authentication (SPF, DKIM, DMARC), warmup, and a way to load the mailboxes into tools such as Instantly or Smartlead. Providers differ most in what the mailbox actually is. If you are new to the term, start with what is cold email infrastructure.
The eight criteria that matter
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1. Mailbox type
Real Google Workspace or Microsoft 365 seats send from Google or Microsoft servers, like most business mail. Own SMTP mailboxes send from the provider's servers and IPs and are usually cheaper. Microsoft tenant bundles put many mailboxes in one tenant for a flat fee; ask how they are licensed, because Microsoft's guidance is that shared mailboxes are not meant for direct sign-in.
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2. Deliverability controls
Look for automatic SPF, DKIM and DMARC, sensible limits per mailbox, and warmup that reacts to bounces and complaints. Be wary of any provider that guarantees inbox placement; nobody can.
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3. Ownership
Domains should be registered in your name or transferable, and you should be able to export mailbox credentials. Otherwise switching providers means starting over.
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4. Setup automation
Buying domains, setting DNS, creating mailboxes and exporting to your sequencer should take minutes, not a day of admin work.
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5. Warmup
Included or a separate tool? New mailboxes need roughly two to four weeks of gradual sending before full volume.
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6. Price at your volume
Compare total monthly cost at your real mailbox count, plus domains at about one per 2–3 mailboxes, and check whether low prices need annual prepayment.
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7. Support
When a domain gets flagged you want a human who answers quickly. Check support hours and channels.
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8. Compliance and billing
Your sending must follow Google, Yahoo and Microsoft bulk-sender rules and local law. For finance teams, currency and tax invoices (for example GST in India) matter too.
Providers ranked by fit
Ranking assumes a typical B2B team that wants real Google or Microsoft mailboxes, 10–100 of them, billed monthly. If your priorities differ, re-sort by the column that matters to you.
| # | Provider | Mailbox type | Price / mailbox / month | Strength | Gap |
|---|---|---|---|---|---|
| 1 | ReplyDak | Google Workspace | $3.50 (10), $2.90 (30), $2.69 (100) | Lowest monthly Google price from 30 up; warmup and DNS included; INR + GST | No Microsoft yet, no API, no pre-warmed mailboxes |
| 2 | Zapmail | Google or Microsoft | $3.90 (10), $3.30 (30), $2.99 (100) | Microsoft today, pre-warmed option, API on Pro, placement-test credits | Costs more than ReplyDak at each size |
| 3 | Inboxkit | Google or Microsoft; Azure tenant | $3 monthly, $2.50 annual | Cheapest Google/Microsoft seats on annual billing | Best price needs a 12-month prepay |
| 4 | Premium Inboxes | Google or Microsoft, done for you | $3.50 → $2.80 by volume | Hands-off setup and sequencer upload | Volume discounts start at 250 |
| 5 | Cheap Inboxes | Google Workspace | $3.50 → $2.80 by volume | Simple Google pricing, cheap domains | Few Microsoft details published |
| 6 | Primeforge | Google or Microsoft | $4.50 per slot | Fits the Salesforge suite | Highest price in this list |
| 7 | ScaledMail | Google; Microsoft per domain | $3.50 Google; $50 per domain for 25 Microsoft | Cheap Microsoft per mailbox | 25 mailboxes on one domain concentrates risk |
| 8 | Mailforge | Own infrastructure, shared IPs | $3 per slot | Low cost, Salesforge suite | Shared IP pool, not Google/Microsoft |
| 9 | Infraforge | Own infrastructure, dedicated IPs | $4 per slot + $99 per IP | IPs you control | Needs volume to justify IP cost |
| 10 | Maildoso | Own SMTP servers and IPs | $2.50 (30) → $0.49 (1,000) | Lowest unit cost at scale | Not Google/Microsoft; test placement first |
Quick picks
| If you need… | Look at |
|---|---|
| Google Workspace, billed monthly, lowest price at 30–100 | ReplyDak |
| Microsoft 365 mailboxes now | Zapmail, Inboxkit, Primeforge, Premium Inboxes |
| To send from day one | Zapmail (pre-warmed mailboxes) |
| An API to create mailboxes from your app | Zapmail (Pro) |
| Lowest price with a 12-month commitment | Inboxkit annual |
| Thousands of mailboxes at minimum cost | Maildoso |
| Rupee billing with a GST invoice | ReplyDak |
Red flags when choosing a provider
- Promises of guaranteed inbox placement or a fixed open rate.
- Domains registered in the provider's name with no transfer option.
- No way to export mailbox credentials to your own sequencer.
- Advice to send hundreds of emails a day from each new mailbox. Read cold email sending limits.
- No mention of SPF, DKIM, DMARC or the bulk sender requirements.
See what your setup costs in ReplyDak: domains, Google mailboxes and warmup in one monthly bill.
Domains, DNS, Google Workspace mailboxes and warmup. From $2.69 per mailbox ($35 for 10).
All product names are trademarks of their respective owners. ReplyDak is not affiliated with any provider listed here.
FAQ
Should I use Google Workspace mailboxes or SMTP mailboxes for cold email?
Google Workspace (or Microsoft 365) mailboxes send from the same servers your prospects' own mail comes from and cost about $2.50–$4.50 each. SMTP mailboxes are cheaper, especially at high volume, but depend on the provider's IP reputation. Many teams start with Google or Microsoft seats and test SMTP only for extra volume.
How many mailboxes do I need to start cold email?
Divide your daily send target by about 30 emails per warmed mailbox. For 300 emails a day that is 10 mailboxes on 4–5 domains. See how many mailboxes per domain.
Does any provider guarantee inbox placement?
No honest provider can. Placement depends on your list, content, volume and recipients' reactions as much as on the infrastructure.
What does a full cold email setup cost per month?
For 10 Google mailboxes on 4 domains, roughly $35–$45 for mailboxes plus about $4–5 a month in domains, before your sequencer. See cold email infrastructure cost.