TL;DR
- Cost per inbox per month ranges from roughly $0.40 to $4.50 across this category, which means a 1,000-inbox programme costs between $500 and $4,500 per month for what looks like the same thing. The difference is real and it is about IP isolation and provider type.
- Maildoso is the strongest fit for high-volume SMTP infrastructure at the lowest cost, from $0.49 per mailbox at scale, with documented domain reputation caveats.
- Mailreef is the strongest fit for teams wanting dedicated mail servers and IPs, at $240 per month on a twelve-month commitment or $249 month-to-month, plus $0.001 per send.
- Primeforge and Zapmail are the strongest fits where real Google Workspace or Microsoft 365 mailboxes are required rather than SMTP relays.
- SMTP is cheaper and Google Workspace generally reaches the inbox more reliably. One published 300,000-email split test found SMTP at $1.40 per mailbox produced a 2.3% reply rate against Google Workspace at $3.00 producing 1.8%, which inverts the usual assumption and is worth testing yourself.
Contents
- What cold email infrastructure actually is
- SMTP versus real mailboxes
- Comparison table: cost per inbox and provider type
- The 8 providers reviewed
- Cost at 1,000 inboxes
- Domain reputation and the risks nobody advertises
- Sending limits and compliance in 2026
- Which provider fits which programme
- FAQ
What cold email infrastructure actually is
A sequencer sends your emails. Infrastructure is what it sends them from: the domains, the mailboxes, the IP addresses, and the DNS authentication records that determine whether your message reaches an inbox or a spam folder.
Running cold email at volume means you cannot send from your primary domain. A deliverability problem on a cold campaign would damage the domain your invoices and support emails depend on. So the standard architecture uses secondary domains, each hosting a small number of mailboxes, each sending a low daily volume, with authentication configured correctly and reputation warmed before real sending begins.
Infrastructure providers sell that architecture as a service. You buy domains and mailboxes at a per-unit price, they configure SPF, DKIM, and DMARC automatically, and you connect the result to Instantly, Smartlead, or Lemlist.
The reason this is a category rather than a checkbox is that doing it manually at 200 mailboxes is genuinely a full-time job, and doing it badly burns domains you have already paid for.
SMTP versus real mailboxes
This is the fork in the road and it determines both your cost and your deliverability ceiling.
SMTP relays are mail servers configured to send on your behalf. They are cheap, often under $1 per mailbox, and they scale instantly. The trade is that receiving providers know an SMTP relay is not a real person's mailbox, and reputation depends heavily on the provider keeping their IP ranges clean, which is outside your control.
Real Google Workspace or Microsoft 365 mailboxes are genuine accounts on the platforms your recipients themselves use. They cost $3.00 to $4.50 per mailbox and take longer to provision. The advantage is ESP matching: a message from a Google Workspace mailbox to a Gmail recipient travels a path that receiving filters treat more favourably.
The conventional wisdom is that Google Workspace delivers better and SMTP delivers cheaper. One published split test across 300,000 emails complicates that: SMTP at $1.40 per mailbox produced a 2.3% reply rate at a cost per reply of $0.10, while Google Workspace at $3.00 per mailbox produced 1.8% at $0.28 per reply. A single test is not proof, and the result probably says as much about that particular SMTP provider's IP hygiene as about the architecture. But it is a good reason to test rather than assume.
The practical position we take: use real mailboxes for high-value target accounts where a single deliverability failure is costly, and SMTP for volume where the economics dominate.
Comparison table: cost per inbox and provider type
| Provider | Type | Cost per inbox per month | Dedicated IP | Domains included |
|---|---|---|---|---|
| Maildoso | SMTP and Google Workspace | $0.49 to $3.10 | Shared pools | Free on quarterly, else $12/yr |
| Mailreef | Dedicated server SMTP | ~$1.60 at 150 mailboxes | Yes | Bring your own |
| Zapmail | Google and Microsoft | $2.40 to $8.00 | Provider-managed | $15/yr |
| Hypertide | Microsoft and Entra | ~$1.00 to $10.00 | Isolated Azure tenant | Included |
| Primeforge | Google and Microsoft 365 | $3.50 to $4.50 | Provider-managed | Extra |
| Infraforge | SMTP | $4.00 plus $14/yr per domain | Yes | $14/yr per .com |
| Mailforge | SMTP shared IP | $2.00 to $3.00 | Shared | Extra |
| MailDeck | SMTP and Google Workspace | $0.50 to $3.90 | Shared | Extra |
| Provider | Entry price | API access | Setup time | Money-back |
|---|---|---|---|---|
| Maildoso | $75/mo for 30 mailboxes | All plans | Fast | 30 days, monthly SMTP |
| Mailreef | $240/mo Agency | Yes | Demand-screened | Not published |
| Zapmail | $39/mo for 10 mailboxes | Pro tier only | Fast | Not published |
| Hypertide | $39/mo | Yes | 4 to 6 hours | Not published |
| Primeforge | ~$4.50/mailbox | Yes | Moderate | Not published |
| Infraforge | $4/mailbox slot | Yes | Moderate | Not published |
| Mailforge | ~$3/mailbox | Yes | Fast | Not published |
| MailDeck | ~$0.50/inbox SMTP | Yes | Fast | Not published |
The 8 providers reviewed
1. Maildoso
Best for: High-volume programmes where cost per inbox is the binding constraint and you can monitor domain reputation yourself.
Maildoso is the cheapest credible option at scale, with a floor of $0.49 per mailbox, full API access on every plan, and self-healing mailboxes that automatically pause inboxes showing reputation damage for fourteen days.
Pricing: Monthly SMTP at $75 for 30 mailboxes at $2.50 each, $158 for 70 at $2.25, and $570 for 300 at $1.90. Other listings cite 30 for $75, 300 for $225 at $0.75, and 1,000 for $499 at $0.50. Quarterly SMTP at $299 for 32 mailboxes at an effective $3.10 per month, $499 for 68 at $2.40, and $2,199 for 400 at $1.80. Combined SMTP and Google Workspace from $90 per month for 15 plus 15 at $3.00 each. Domains are free on quarterly plans and $12 per year otherwise. No setup fee, and a 30-day money-back guarantee on monthly SMTP. Sending is capped at 15 per day per mailbox.
Maildoso operates a stated no-discount policy, though one documented user account reports negotiating from $1.90 to $1.40 per mailbox at 500 mailboxes.
Where it falls short: This is where the honest assessment matters. User reports document burned .xyz and .click domains, SURBL blocklisting, a 2025 blacklist incident, and support described as reactive. Shared IP pools mean another customer's behaviour affects your deliverability. If you buy Maildoso, monitor blocklist status yourself rather than relying on the provider to tell you.
Verdict: The best cost per inbox available, with real reputation risk attached. Appropriate for experienced teams that monitor deliverability actively. Not appropriate as a set-and-forget purchase.
2. Mailreef
Best for: Agencies and teams that want dedicated mail servers and dedicated IPs rather than shared pools.
Mailreef's architecture is the differentiator. Each customer gets a dedicated mail server with a dedicated IP, which removes the shared-pool reputation risk that affects cheaper providers. It also screens customers for spammers before onboarding, which protects the IP ranges of everyone already on the platform.
Pricing: Agency at $240 per month on a twelve-month commitment plus $0.001 per send. Agency Flex at $249 per month month-to-month plus $0.001 per send. Enterprise custom. Each server includes 150 mailboxes, bring-your-own domains, automatic SPF, DKIM, and DMARC configuration, and full API access. Caps are 100,000 emails per month, 50 domains, and 200 mailboxes per server, after which another server costs a further $249.
Mailreef recommends a maximum of 3 mailboxes per domain, 50 sends per mailbox, and a 1:1 ratio of cold to warm activity.
Where it falls short: Microsoft Outlook and SMTP only, with no Google Workspace option, which rules it out if your prospects are predominantly on Gmail and you want ESP matching. It requires a demo and passes you through spammer screening, so provisioning is slower. The $0.001 per send charge is small but should be modelled at volume: 100,000 emails per month adds $100.
Verdict: The strongest fit where deliverability matters more than cost per inbox, and the dedicated IP is worth paying for. At 150 mailboxes the effective cost of roughly $1.60 each is genuinely competitive given what you get.
3. Zapmail
Best for: Teams that want real Google Workspace or Microsoft mailboxes with the option of pre-warmed inboxes.
Zapmail sells both provisioning and pre-warming, which shortens time to first send considerably. It also offers US and EU IP options, which matters for regional targeting.
Pricing: Google and Microsoft plans are Starter at $39 per month for 10 mailboxes with extras at $3.50 and 20 exports, Growth at $99 for 30 with extras at $3.25 and 60 exports, and Pro at $299 for 100 with extras at $3.00, 200 exports, priority support, and API access. Pre-warmed plans are Starter at $39 for the first month then $24 per month for 3 inboxes with extras at $8.00, Growth at $149 then $84 for 12 with extras at $7.00, and Pro at $339 then $180 for 30 with extras at $6.00. Domains are $15 per year. Quarterly and yearly billing includes two months free.
Where it falls short: API access is restricted to the Pro tier, which is a meaningful constraint if you want to automate provisioning at smaller volumes. Pre-warmed inboxes cost roughly double, which is defensible but should be compared against three weeks of your own warm-up time.
Verdict: The most flexible provider here, and the pre-warmed option is genuinely useful when you need to launch a campaign quickly.
4. Hypertide
Best for: Teams wanting fast provisioning on isolated Microsoft infrastructure.
Hypertide provisions Google Workspace, Microsoft 365, and Entra or Azure mailboxes, with each order placed on its own isolated Azure tenant with dedicated domains and rotating Microsoft IPs. Setup completes in four to six hours according to most sources, with some claiming under ten minutes. Automatic SPF, DKIM, and DMARC configuration and built-in AI warm-up are included, and it integrates with Instantly, Smartlead, Lemlist, Apollo, and HubSpot.
Pricing: From $39 per month, also cited at $50 per month for 5,000 emails per month per order.
Where it falls short: Two caution flags. The company has only four employees and roughly 789 LinkedIn followers, which is a vendor continuity risk on infrastructure you depend on. And a competitor characterises it as a basic rotation tool with shared pools, which contradicts the isolated tenant claim. Treat both claims sceptically and ask directly during evaluation. The stated ability to send at 5,000 per month after only 50% of normal warm-up is also aggressive and worth questioning.
Verdict: Fast and cheap with genuine unanswered questions about scale and isolation. Suitable for testing, harder to justify for a programme you cannot afford to interrupt.
5. Primeforge
Best for: Programmes where real Google Workspace and Microsoft 365 mailboxes with ESP matching are a requirement.
Primeforge provisions genuine Google Workspace and Microsoft 365 accounts with ESP matching, meaning Gmail-hosted mailboxes send to Gmail recipients and Microsoft to Microsoft. That path alignment is the strongest structural deliverability advantage available.
Pricing: $3.50 to $4.50 per mailbox per month.
Where it falls short: It is among the most expensive per inbox here, roughly seven to nine times Maildoso's floor. At 1,000 inboxes that is $4,500 per month against $500. Provisioning real accounts also takes longer than spinning up SMTP.
Verdict: The right choice when deliverability on high-value accounts justifies the premium. The wrong choice for volume-led programmes where cost per reply is the metric.
6. Infraforge
Best for: Teams wanting dedicated IPs on SMTP with granular domain-level control.
Infraforge sells mailbox slots with dedicated IPs, domain registration, and optional SSL and domain masking.
Pricing: $4.00 per mailbox slot per month plus $14 per year for each .com domain. SSL and domain masking cost $2 per domain per month on quarterly billing or $0.50 on annual. Annual billing includes two months free.
Where it falls short: At $4.00 per slot it is priced like a real-mailbox provider while delivering SMTP, which is a difficult position to defend unless the dedicated IP is specifically what you are buying. Domain costs are separate and add up at scale.
Verdict: Justified where you want dedicated IPs but do not need Google Workspace. Compare directly against Mailreef, which offers dedicated servers at a lower effective per-mailbox cost.
7. Mailforge
Best for: Mid-volume SMTP programmes wanting a simple flat per-mailbox price.
Mailforge is straightforward shared-IP SMTP at $2.00 to $3.00 per mailbox, sitting between Maildoso's floor and the real-mailbox providers.
Where it falls short: Shared IP pools carry the same reputation exposure as Maildoso without Maildoso's price advantage. No dedicated IP option.
Verdict: A reasonable middle option with no standout characteristic. Choose it for simplicity rather than for economics or deliverability.
8. MailDeck
Best for: Teams wanting the lowest SMTP price with the option of real Google Workspace or Outlook tenants alongside.
MailDeck spans both architectures: SMTP from $0.50 per inbox under 1,000 units, Google Workspace at $2.99 to $3.90 per inbox, and Outlook tenants at $30 to $40 per tenant. It claims over 650,000 inboxes provisioned for more than 1,500 clients at 98% inbox placement.
Where it falls short: The 98% inbox placement figure is vendor-published with no methodology disclosed, and inbox placement claims in this category should be treated as marketing until you have tested your own sending. Shared IP pools on the SMTP product.
Verdict: Competitive on price at both ends of the architecture split. Verify the placement claim with your own seed testing rather than accepting it.
Cost at 1,000 inboxes
The per-unit differences compound dramatically at scale. Published comparisons of a 1,000-inbox programme put the range at $500 to $4,500 per month.
| Provider | Architecture | Monthly cost at 1,000 inboxes |
|---|---|---|
| MailDeck SMTP | Shared IP SMTP | ~$500 |
| Maildoso | Shared IP SMTP | ~$499 to $1,900 |
| Mailin | SMTP | ~$1,490 |
| Mailreef | Dedicated server, 5 servers | ~$1,200 plus per-send |
| Mailforge | Shared IP SMTP | ~$3,000 |
| Infraforge | Dedicated IP SMTP | ~$4,000 |
| Primeforge | Real Google and Microsoft | ~$4,500 |
At the other end of the scale, a solo founder sending 50,000 emails per month should budget roughly $123 to $453 per month across infrastructure, sequencer, and verification combined.
The number that actually matters is not cost per inbox. It is cost per reply. The 300,000-email split test cited earlier produced $0.10 per reply on SMTP against $0.28 on Google Workspace, a difference that swamps the per-inbox comparison entirely. Model cost per reply for your own programme before optimising cost per inbox.
Domain reputation and the risks nobody advertises
Three failure modes account for most infrastructure disasters, and none of them appear on a pricing page.
Cheap TLD burn. Providers that supply .xyz, .click, and similar low-cost TLDs are giving you domains that receiving filters already distrust, because those TLDs carry disproportionate spam volume. Documented Maildoso complaints centre on exactly this. Insist on .com or .co domains even at higher cost, because a $12 domain that lands in spam is more expensive than a $30 one that does not.
Shared IP contamination. On any shared-pool provider, your deliverability depends on the behaviour of every other customer on that IP range. When one of them sends something egregious, the range gets blocklisted and your campaign stops working through no fault of your own. This is the structural argument for Mailreef's dedicated servers and for Hypertide's isolated tenant claim. It is also why Mailreef screens customers before onboarding, which is a feature disguised as friction.
Blocklist monitoring gaps. Discovering you are on SURBL or Spamhaus three weeks late means three weeks of wasted sending. Most providers do not proactively alert you. Set up your own monitoring on every domain you send from, and treat the provider's monitoring as a supplement rather than the primary control.
The general principle: infrastructure is the one part of the outbound stack where the cheapest option can cost you the most, because a burned domain is a sunk cost and a damaged sending reputation takes months to rebuild.
Sending limits and compliance in 2026
Google and Yahoo bulk sender requirements apply at 5,000 or more messages per day to their users. They mandate SPF, DKIM, and DMARC authentication, one-click unsubscribe conforming to RFC 8058 honoured within two days, and TLS encryption in transit. Spam complaint rates must stay below 0.10% and must never reach 0.30%.
Those thresholds have practical consequences for how you configure infrastructure. At a 0.10% ceiling, 5,000 daily sends allows five complaints. That is a very small margin, and it is the real reason for low per-mailbox daily limits rather than any technical constraint.
Sensible operating parameters across the providers here: 15 to 50 sends per mailbox per day depending on provider guidance, a maximum of 3 mailboxes per domain as Mailreef recommends, and roughly three weeks of warm-up before full volume. Unify's default of 25 emails per mailbox per day, configurable to 65, is a reasonable reference point from a vendor with no incentive to understate.
One provider claim worth questioning specifically: Hypertide's stated ability to send at 5,000 per month after only 50% of normal warm-up. Compressed warm-up is exactly the behaviour that generates complaints, and complaints are the metric that ends programmes.
Which provider fits which programme
| Situation | Strongest fit | Why |
|---|---|---|
| Volume-led, cost per inbox critical | Maildoso or MailDeck | ~$0.50 per inbox at scale |
| Deliverability critical, want dedicated IPs | Mailreef | Dedicated server and IP, customer screening |
| Need real Google Workspace with ESP matching | Primeforge | Genuine accounts, path alignment |
| Want pre-warmed inboxes to launch fast | Zapmail | Pre-warmed plans, US and EU IPs |
| Microsoft-heavy prospect base | Mailreef or Hypertide | Outlook and Entra focus |
| Agency running multiple clients | Mailreef | Per-server isolation between clients |
| Testing before committing | Maildoso | 30-day money-back on monthly SMTP |
| Small programme under 50 mailboxes | Zapmail Starter | $39 per month for 10 mailboxes |
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FAQ: Cold Email Infrastructure Providers
How much does cold email infrastructure cost per inbox?
The range is roughly $0.40 to $4.50 per inbox per month. SMTP relays sit at the low end, from $0.49 on Maildoso and around $0.50 on MailDeck. Real Google Workspace and Microsoft 365 mailboxes sit at the high end, $3.00 to $4.50 on Primeforge and Zapmail. A 1,000-inbox programme therefore costs between $500 and $4,500 per month.
Is SMTP or Google Workspace better for cold email?
Google Workspace generally delivers better because of ESP matching, where a Gmail-hosted mailbox sending to a Gmail recipient travels a more trusted path. However, one published 300,000-email split test found SMTP at $1.40 per mailbox produced a 2.3% reply rate at $0.10 per reply against Google Workspace at $3.00 producing 1.8% at $0.28 per reply. Test rather than assume.
What are the Google and Yahoo bulk sender rules?
They apply at 5,000 or more messages per day to Gmail or Yahoo users and require SPF, DKIM, and DMARC authentication, one-click unsubscribe conforming to RFC 8058 honoured within two days, and TLS encryption. Spam complaint rates must stay below 0.10% and must never reach 0.30%.
How many mailboxes should I put on one domain?
Mailreef recommends a maximum of three mailboxes per domain, which is the most conservative published guidance and a sensible default. Concentrating more mailboxes on fewer domains increases the damage when a single domain's reputation degrades.
How many emails per day can I send from one mailbox?
Provider guidance ranges from 15 per day on Maildoso to 50 on Mailreef. Unify defaults to 25 per mailbox per day, configurable up to 65. Allow roughly three weeks of warm-up before reaching full volume. Lower limits exist because Google's 0.10% complaint ceiling leaves very little margin.
Why do some providers burn domains?
The most common cause is supplying cheap TLDs such as .xyz and .click, which receiving filters already distrust because of disproportionate spam volume. The second cause is shared IP pools, where another customer's behaviour blocklists a range you also send from. Insist on .com or .co domains and monitor blocklist status on every sending domain yourself.
Yananai A. Chiwuta
Author
Yananai Chiwuta is a Go-To-Market Architect and founder of Forma Nôrden. He builds Go-To-Market growth systems for B2B companies selling into enterprise and mid-market accounts.
Celine Sky
Reviewer
Celine ensures technical accuracy and strategic alignment across all Forma Nôrden playbooks and resources.
