10 Best Cold Email Infrastructure Providers (2026)

The best cold email infrastructure providers in 2026, ranked:

1. Outreach2day: SMTP mailboxes with warm-up and a sending engine in $2.50 per mailbox a month. Lowest full cost at 25 mailboxes in our table.

2. Inframail: flat monthly plans with unlimited Microsoft-backed inboxes. Best for high counts at a fixed monthly bill.

3. Zapmail: Google Workspace and Microsoft 365 mailboxes in plans of 10, 30 and 100.

4. Mailforge: shared-IP SMTP mailbox slots from $3, down to $2 at volume.

5. InboxKit: Google and Microsoft mailboxes at a flat $3.00, no minimum.

6. Mailreef: dedicated mail servers billed per server plus $0.001 per email.

7. Premium Inboxes: done-for-you Google and Microsoft inboxes, uploaded to your sequencer.

8. Infraforge: private SMTP on dedicated servers and IPs, billed quarterly or yearly.

9. Maildoso: SMTP mailboxes at $2.50 on the 30-mailbox plan, 15 cold emails a day each.

10. Primeforge: Google Workspace and Microsoft 365 slots from $4.50, US IPs.

We make Outreach2day and put it first. That is our decision, not a score. Every other position follows one rule: the monthly cost of a full setup at 100 mailboxes (mailboxes, warm-up and a sending engine), cheapest first; Mailforge and InboxKit tie at 100 and are ordered by the cost at 400. Every competitor fact on this page comes from the vendor's own public page, linked in the table.

Prices checked September 29, 2026, on each vendor's pricing page. Vendors change prices often; if a number here is out of date, write to support@outreach2day.com.

Price Table: 10 Providers Side by Side

List prices on monthly billing unless the row says otherwise. "Warm-up" and "Sending" say whether the mailbox price includes them.

Full Cost at 25, 100 and 400 Mailboxes

The price per mailbox hides the bill. Nine of the ten providers sell no sending engine, and most leave out warm-up, so the real cost is mailboxes plus a sequencer. We price every setup the same way as our provider comparison: 550 cold emails per mailbox a month (25 a day on 22 working days), monthly list prices, domains left out. A provider that sells mailboxes only gets the cheapest Instantly plan that covers the volume, because that plan includes warm-up and sending: Hypergrowth at $97 a month for 125,000 emails, or Hypergrowth plus an add-on at $184 for 250,000.

How the less obvious rows are built:

• Maildoso caps cold email at 15 a day per mailbox, so the same volume needs 42, 167 and 667 Maildoso mailboxes. We price them at $2.50, Maildoso's rate on its 30-mailbox plan.

• Inframail at 400 mailboxes: 220,000 emails a month is above the $147 plan's 80,000, so the row uses the $387 Agency Pack.

• Mailreef bills per server and per email: 13,750, 55,000 and 220,000 emails cost $13.75, $55 and $220. Mailreef lists "150 Mailboxes+/Server" without a hard limit, so the 400-mailbox row assumes one server; ask Mailreef before you plan on it.

• Infraforge has no monthly billing. The row is the monthly equivalent of quarterly billing.

Inframail is $6 a month cheaper than us at 100 mailboxes, and Inframail and Mailreef are cheaper at 400. Flat server and plan pricing wins at high counts if you already accept a separate sequencer and warm-up tool. At 25 mailboxes, a flat plan costs the same as at 100.

The 10 Providers in Detail

1. Outreach2day

What it is. Cold email mailboxes on your own domains, with warm-up, a sending engine (campaigns, sequences, one inbox for replies) and per-mailbox analytics in one subscription. 3,600+ teams have used it since 2024, and 40M+ emails a day go through the platform, cold and warm-up together.

Pricing. $2.50 per mailbox a month, minimum 12 mailboxes ($30). Domains are bought in the app and registered to you: $13 a year for a .com, $5 for a .info. Volume discounts are available for large orders; the terms come from a call with the team. Monthly by card, no contract. See pricing.

Mailbox type. SMTP/IMAP mailboxes, up to 5 per domain. SPF, DKIM and DMARC are set automatically.

Warm-up. Included for as long as you keep the mailbox: 25+ warm-up emails a day to Google recipients, 25 to Outlook and 25 to other providers. Warm-up only for 14 days, then up to 25 cold emails per mailbox a day from day 21.

Best for. Agencies and in-house outbound teams that want mailboxes, warm-up and sending on one bill. Mailboxes also sync to Instantly and Smartlead with an API key, export as CSV in the import format of 14 tools, and are managed through a REST API and a hosted MCP server with OAuth sign-in.

Honest limits. No Google Workspace or Microsoft 365 mailboxes. No free trial. The minimum is 12 mailboxes, so it does not fit a 1–5 mailbox setup. No blacklist monitoring. We do not guarantee inbox placement; we measure it per mailbox with Google and Outlook placement tests.

2. Inframail

What it is. Infrastructure for cold outreach: "unlimited Microsoft-backed inboxes on your own domains", on dedicated US IPs, at a flat monthly price.

Pricing. Unlimited Plan $147 a month (recommended up to 400 mailboxes, 1 dedicated IP, 80,000 emails a month). Agency Pack $387 a month (up to 1,000 mailboxes, 3 dedicated IPs, 300,000 emails a month). Done-for-you $797 a month, 3 months minimum. The yearly toggle says "Save 30%". Domains can be bought in the app, or you connect your own for $5 per domain, once.

Mailbox type. Microsoft-backed inboxes. SPF, DKIM and DMARC, redirects, forwarding and custom tracking domains are set up automatically.

Warm-up. Not in the standard plans. The FAQ recommends warming up new inboxes as you would elsewhere. The $797 plan includes warm-up.

Best for. Teams that already run a sequencer and a warm-up tool and need hundreds of inboxes at one fixed price.

Honest limits. The plans cap emails a month, so the flat price holds only inside the cap. No sending engine outside the $797 plan. The home page shows a "Money-back guarantee" label; we found no terms for it.

3. Zapmail

What it is. Google Workspace and Microsoft 365 mailboxes with automated DNS, sold in plans. No sequencer; ZapBox is a free unified inbox for replies.

Pricing. Monthly: Starter $39 (10 mailboxes, extra $3.50), Growth $99 (30, extra $3.25), Pro $299 (100, extra $3.00). Quarterly and yearly billing cost less; the headline "from $2.50" is the yearly Pro rate. Domains: .com $13, owned by you. No refunds.

Mailbox type. Google Workspace or Microsoft 365 on US/EU IPs, same prices for both.

Warm-up. Zapmail's FAQ says setup, DNS, warm-up and health monitoring are handled for you. No separate warm-up price.

Best for. Buyers who want Google or Microsoft mailboxes and send from Instantly, Smartlead or another of the 50+ tools it exports to.

Honest limits. No sending engine. API access only on the Pro plan. No refunds. The pre-warmed plans were shown out of stock with a waitlist.

4. Mailforge

What it is. SMTP mailbox slots on shared infrastructure, from the Forge group. Warm-up (Warmforge) and sending (Salesforge) are separate Forge products; Google and Microsoft mailboxes are sold under Primeforge.

Pricing. $3 per slot a month for the first 10 and up to 100 add-on slots, $0.10 less per 100 add-on slots after that, $2 above 1,000. Minimum 10 slots ($30). Yearly billing gives 2 months free. You pay per slot, not per active mailbox. SSL and domain masking cost $2 per domain a month or $6 a year. Domains: .com $14 a year.

Mailbox type. SMTP on shared IPs.

Warm-up. Warmforge, billed separately unless you use Salesforge.

Best for. Senders who want cheap SMTP slots and plan to run Salesforge or another sequencer anyway.

Honest limits. Warm-up, sending and placement tests are separate bills. Mailforge recommends 30 emails per mailbox a day and 2–3 mailboxes per domain. No free trial.

5. InboxKit

What it is. Google Workspace, Microsoft 365 and Azure tenant mailboxes at one flat price per mailbox.

Pricing. $3.00 per mailbox a month, $2.70 quarterly, $2.50 on annual billing, same for Google and Microsoft. No minimum and no plans. Azure is $30 per tenant a month for up to 100 mailboxes. Domains from $2 a year.

Mailbox type. Google Workspace or Microsoft 365, with admin access per domain.

Warm-up. An add-on at $3 per mailbox a month, which doubles the monthly price.

Best for. Small setups that need a handful of Google or Microsoft mailboxes, and teams that bill yearly.

Honest limits. No sending engine. Blacklist checks and placement tests are in the InfraGuard add-on, priced per domain. Subscriptions are generally non-refundable.

6. Mailreef

What it is. A dedicated mail server with a dedicated IP, with mailboxes you create on it. Integrates with Smartlead and Instantly.

Pricing. Agency Flex $249 a month, month to month, plus $0.001 per email sent. Agency $240 a month on a 12-month commitment, plus $0.001 per email. Enterprise by quote. Domains: bring your own or buy in one click; we found no domain price.

Mailbox type. SMTP on your own server and IP, "150 Mailboxes+/Server".

Warm-up. Mailreef recommends a 1:1 ratio of cold to warm-up emails and lists pre-warmed servers, domains and mailboxes. It does not state which warm-up tool runs.

Best for. Senders who want an IP no one else sends from, at high volume.

Honest limits. A dedicated IP carries only your reputation, good or bad. No sending engine. Mailreef recommends at most 3 mailboxes per domain and 50 emails per mailbox. We found no free trial or refund terms.

7. Premium Inboxes

What it is. A reseller of Google Workspace and Microsoft 365 inboxes, set up by hand and uploaded to your sequencer.

Pricing. $3.50 per inbox (1–249), $3.00 (250–1,249), $2.80 (1,250+). "Insured Infrastructure" is $4.50 an inbox. The Operations tier, with placement tests and blacklist monitoring, is $7,500 a month with inboxes not included.

Mailbox type. Google Workspace or Microsoft 365, live in under 6 hours.

Warm-up. Switched on in your sequencer during setup; no separate price.

Best for. Teams on Instantly, Smartlead, Apollo, Lemlist, Reply.io or Bison that want Google or Microsoft inboxes delivered ready to use, with free replacements.

Honest limits. No sending engine. The site recommends at most 15 cold emails per inbox a day, which means more inboxes for the same volume. It says both that you bring your own domains and that it can supply them. No refunds once a license is activated.

8. Infraforge

What it is. Private SMTP infrastructure on dedicated servers and IPs, from the Forge group.

Pricing. $4 per slot a month on quarterly billing, falling to $3 above 1,000 add-on slots; yearly billing lowers it further. There is no monthly billing. Minimum 10 slots. Extra dedicated IPs cost $99 per IP a month. SSL and masking $2 per domain a month. Domains: .com $14 a year.

Mailbox type. SMTP on dedicated servers and IPs.

Warm-up. Warmforge, a separate product.

Best for. Teams that want dedicated IPs inside the Forge stack and can commit to a quarter.

Honest limits. Quarterly or yearly billing only. Warm-up and sending are separate bills. No free trial.

9. Maildoso

What it is. SMTP mailboxes on Maildoso's own servers and IPs, with IP rotation. No warm-up and no sending engine.

Pricing. $2.50 per mailbox on the 30-mailbox plan, $75 a month. Larger plans and custom counts are sold on the pricing page and in the app. Maildoso has a no-discount policy. Domains are $12 a year, $15 from October 1, 2026.

Mailbox type. SMTP on Maildoso's servers and IPs.

Warm-up. Not included. Maildoso asks for at least 14 days of warm-up with an outside provider or the Instantly pool before the first campaign.

Best for. Teams already paying for Instantly, Smartlead or EmailBison that want SMTP mailboxes synced to it, plus an API and MCP server.

Honest limits. Up to 15 cold emails per mailbox a day, so the same volume needs more mailboxes. Domains stay registered with Maildoso while you use it. The 30-day money-back guarantee is narrowed in the terms to mailboxes that fail to send for 3 or more days through Maildoso's fault.

10. Primeforge

What it is. Google Workspace and Microsoft 365 mailboxes set up for cold email, from the Forge group: "Those are specifically Google Workspace and MS365 mailboxes with US IP addresses."

Pricing. $4.50 per slot a month on monthly billing, down to $3.50 above 1,000 add-on slots, or $3.75 a month billed yearly. Minimum 10 slots. Domains: .com $14 a year. For 25 mailboxes the calculator shows $113 a month billed monthly.

Mailbox type. Google Workspace or Microsoft 365, one Microsoft tenant per domain.

Warm-up. Warmforge: $12 per slot a month on monthly billing for up to 10 slots, less at higher volumes; included if you send through Salesforge.

Best for. Teams on Salesforge that want Google or Microsoft mailboxes with US IPs.

Honest limits. $4.50 a slot is the top of the price range in this list. Warm-up, sending and placement tests are separate. No free trial.

What Matters When Choosing

Check these before you compare logos or review scores:

1. Full monthly cost. Mailboxes plus warm-up plus a sending engine, at your mailbox count. The table above shows how far it moves from the price per mailbox.

2. Mailbox type. SMTP/IMAP, Google Workspace or Microsoft 365. Each has different prices and rules; see below.

3. Cold emails per mailbox a day. Providers state 15, 25, 30 or 50. A lower number means more mailboxes for the same volume.

4. Mailboxes per domain. Recommendations run from 2–3 (Mailforge) to 3 (Mailreef) to 5 (Outreach2day). This sets how many domains you buy.

5. Warm-up. Included, an add-on, or your own tool, and for how long it keeps running after launch.

6. Minimum order and billing. 1, 10, 12 or 30 mailboxes; monthly, quarterly or yearly.

7. Domain ownership. Whether domains bought through the provider are registered to you, and whether you can move them.

8. Portability. API, CSV export, and which sequencers the mailboxes connect to.

9. Monitoring. Placement tests, blacklist checks and per-mailbox stats: included, add-on or missing.

10. Refunds and trials. Most providers here offer neither. Read the refund page before a large order.

For the same checks written as buyer questions, see our checklist for buying cold email mailboxes.

Shared vs Dedicated IPs

Every email leaves from an IP address, and mailbox providers judge that IP along with your domain and your content.

• Shared IPs. Many customers send from the same pool. Mailforge sells SMTP on shared infrastructure. The pool's reputation depends on everyone in it, and the cost is lower.

• Dedicated IPs. Only you send from the IP. Infraforge, Mailreef and Inframail sell dedicated IPs; Infraforge charges $99 a month for each extra one. The reputation is yours alone: clean sending keeps it, and a bad list or a spam complaint spike is not diluted by anyone else's traffic.

• Google and Microsoft. Workspace and Microsoft 365 mailboxes send from Google's and Microsoft's own servers. You do not choose the IP.

A dedicated IP helps when you send steady volume from clean lists and want no neighbours. It does not fix a weak list or copy that gets marked as spam. Whatever you pick, measure placement per mailbox and per recipient provider, and pause mailboxes whose numbers drop.

SMTP Mailboxes vs Google Workspace and Microsoft 365

SMTP/IMAP mailboxes are standard mailboxes on your domain, hosted by the infrastructure provider. They connect to any sequencer over SMTP and IMAP. Where they are priced per mailbox in this list, they cost $2 to $4 a month, and the provider sets the sending rules. Outreach2day, Mailforge, Infraforge, Maildoso and Mailreef sell this type.

Google Workspace and Microsoft 365 mailboxes are business accounts on Google's or Microsoft's platform, bought through a reseller. Here they cost $2.50 (InboxKit, annual billing) to $4.50 a month (Primeforge). Google and Microsoft set the sending limits and the terms of use. Details: Google Workspace sending limits and Microsoft 365 sending limits.

Pick Google or Microsoft if a client or your team requires those accounts. Pick SMTP if you want the lowest cost per mailbox and more control over volume. Many senders run both and split campaigns by recipient provider. Our guide to Google Workspace alternatives for cold email covers the trade-offs in more detail.

Verdict

• One bill for mailboxes, warm-up and sending: Outreach2day, $2.50 per mailbox, lowest full cost at 25 mailboxes in our table and within $6 of the lowest at 100.

• Hundreds of inboxes at a fixed price, sequencer already paid for: Inframail or Mailreef.

• Google Workspace or Microsoft 365 required: Zapmail or InboxKit for price, Premium Inboxes for done-for-you delivery, Primeforge inside the Forge stack.

• Cheap SMTP slots with Salesforge: Mailforge; with dedicated IPs, Infraforge.

• SMTP mailboxes synced to a sequencer you already use, at up to 15 a day: Maildoso.

The scored version of this comparison, with published weights, is on /compare. Every vendor's plans are broken down in its own pricing post, for example Mailforge pricing and Zapmail pricing.

FAQ

What is the 30/30/50 rule for cold emails?

There is no single definition. Pages that use the name split cold email effort in different ways, for example 30% research, 30% personalization and 50% follow-up, or 30% personalization, 30% value and 50% call to action. The shares add up to 110%, so read it as a reminder to invest in follow-up, not as a formula. It says nothing about infrastructure. The numbers that affect deliverability are volume per mailbox (up to 25 cold emails a day), mailboxes per domain (up to 5) and warm-up before launch (14 days).

What is the best platform for cold outreach?

For infrastructure, pick by full monthly cost and mailbox type. Outreach2day includes mailboxes, warm-up and a sending engine for $2.50 per mailbox a month. If you need Google Workspace or Microsoft 365 accounts, Zapmail, InboxKit and Premium Inboxes sell them, and you add a sequencer such as Instantly or Smartlead.

How many mailboxes do I need for cold email?

Divide your daily cold email target by 25. For 1,000 cold emails a day you need 40 mailboxes. Add a few spare ones, and create them at least three weeks before you need full volume. Worked examples: how many mailboxes do I need.

How many mailboxes should I put on one domain?

Up to 5 at Outreach2day. Other providers recommend fewer: 2–3 at Mailforge, 3 at Mailreef. 40 mailboxes at 5 per domain means 8 domains. See mailboxes per domain.

How many cold emails can one mailbox send per day?

We recommend up to 25 cold emails per mailbox a day, not counting warm-up. Providers' own numbers differ: Maildoso caps at 15, Premium Inboxes recommends 15, Mailforge 30, and Mailreef and Inframail list 50 per mailbox. More detail: cold emails per mailbox per day.

How much does cold email infrastructure cost?

For 100 mailboxes with warm-up and a sending engine, $244 to $547 a month in this list, and $250 with Outreach2day. The mailbox line alone runs from $2 to $4.50 per mailbox a month. Domains are extra: $13 a year for a .com with us, $12 to $14 at most providers here. A full breakdown of the other costs is in how much cold email costs.

Sources

Checked September 29, 2026:

• Outreach2day pricing and facts for AI assistants: our prices, limits and warm-up volume.

• Inframail: plans, email caps, domains, warm-up, send limit.

• Zapmail: plans, extra mailboxes, domains, refunds.

• Mailforge pricing: slot tiers, minimum, masking, domains, sending recommendation.

• InboxKit pricing: per-mailbox prices, warm-up add-on, Azure.

• Mailreef pricing: plans, per-email fee, server capacity, recommendations.

• Premium Inboxes pricing and home page: tiers, Operations tier, sending recommendation.

• Infraforge pricing: slot tiers, billing, dedicated IPs.

• Maildoso pricing: plan, sending cap, domains, warm-up.

• Primeforge pricing: slot tiers, minimum, domains.

• Warmforge pricing: warm-up slots for Mailforge, Infraforge and Primeforge.

• Instantly pricing: the sending plan added to mailbox-only providers.