Mailboxes for Cold Email: A Buyer's Checklist

Buy mailboxes for cold email from a provider that puts them on domains you own, includes or supports warm-up, states a daily cold email limit, and lets you take the mailboxes to any sequencer. Judge the offer by the full monthly cost, mailboxes plus warm-up plus a sending tool, not by the price per mailbox. The ten checks below cover what vendors' pricing pages leave out.

We make Outreach2day, which sells cold email mailboxes. Our answers to the checklist come from our own pricing and FAQ; everyone else's come from their public pages.

The 10 Things to Check Before You Buy

1. Mailbox type. Google Workspace, Microsoft 365 or SMTP/IMAP. Each has a different price and different rules; the trade-offs are in Google Workspace alternatives for cold email and SMTP for cold email. Ask for real mailboxes with IMAP, not a sending relay.

2. What the price includes. Mailbox only, or also warm-up, a sending engine and an inbox for replies. Each missing piece is another subscription.

3. Minimum order. Some vendors start at one mailbox, others at 10, 12, 30 or 75. Check the smallest bill, not only the unit price.

4. The daily cold limit the vendor recommends. This decides how many mailboxes you need for your volume. A vendor that recommends 15 a day needs more mailboxes than one that recommends 25 for the same number of emails.

5. Mailboxes per domain. We recommend up to 5, and Instantly caps its done-for-you domains at 5; see how many mailboxes to put on one domain. More per domain puts more mailboxes at risk when one domain's reputation drops.

6. Domain ownership and transfer. Who is the registrant, and can you move the domains to your own registrar account? If the vendor keeps them, your sending history stays with the vendor.

7. Cancellation. What happens to the mailboxes and domains when you stop paying, and whether there is a contract or a refund.

8. Replacing burned domains. Whether a new domain means buying new mailboxes or reusing the slots you already pay for. See what to do with a burned domain.

9. Export to your sequencer. SMTP/IMAP logins, a direct sync, or a CSV in your tool's import format. Mailboxes that only work inside one platform tie your infrastructure to that platform.

10. API. An API lets you create mailboxes, domains and warm-up in bulk and connect them to your own tools.

How Vendors Answer the Checklist

We make Outreach2day, so it is listed first; the other entries use each vendor's own public pages. "Not stated" means we did not find it on the pages listed in Sources, not that the vendor lacks it.

Read the tables by the checks that matter to you. If you run campaigns in one sequencer for good, platform-only mailboxes may be fine. If you want to switch tools later or run several clients, ownership and export weigh more than a lower unit price.

The True Monthly Cost at 25, 100 and 400 Mailboxes

We use the same model 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 vendor 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. Maildoso caps cold email at 15 a day, so we count the extra Maildoso mailboxes needed for the same volume.

How the rows are built, at 100 mailboxes: Outreach2day is 100 × $2.50 = $250 with warm-up and sending included. InboxKit is 100 × $3.00 = $300 plus Hypergrowth $97 = $397. Maildoso needs 167 mailboxes to send the same 55,000 emails at 15 a day: 167 × $2.50 = $417.50, plus $97 = $514.50. Smartlead is 100 × $4.50 = $450 plus its Pro plan at $94 = $544. Instantly is 100 × $5 = $500 plus Hypergrowth $97 = $597.

If you already pay for a sequencer, subtract its line and compare the mailbox cost alone. Large orders with us can get a volume discount; book a call for bulk pricing.

How Many Mailboxes to Buy

Work backwards from volume. Divide the cold emails you want to send a day by 25 to get mailboxes, then divide by 5 to get domains. At 1,000 cold emails a day: 1,000 ÷ 25 = 40 mailboxes, 40 ÷ 5 = 8 domains. On Outreach2day that is 40 × $2.50 = $100 a month, plus 8 × $13 = $104 a year for .com domains.

Add time: new mailboxes warm up for at least 14 days before any cold email and reach full volume around day 21. Buy capacity before you need it. The capacity calculator runs the numbers for any volume, and how many mailboxes do I need explains the reasoning.

FAQ

What are the best inboxes for cold email?

The ones that pass the checklist for your case: a mailbox type your prospects' providers accept, warm-up included or available, a stated daily limit, domains you own and export to your sequencer. Our scored ranking is on the comparison page.

What is the cheapest way to buy cold email inboxes?

Compare the full stack, not the unit price. A mailbox at the same or a lower price can cost more a month once you add warm-up and a sending tool, or when a lower daily limit means buying more mailboxes.

Should I buy Google Workspace or SMTP inboxes for cold email?

Google Workspace costs more per mailbox and its acceptable use policy bans unsolicited mass email. SMTP inboxes from a cold email provider cost less and are sold for outbound. Keep Workspace if you need only a few mailboxes or the Google apps.

Can I buy just one mailbox for cold email?

Some vendors sell single mailboxes; our minimum is 12 ($30 a month). One mailbox sending up to 25 cold emails a day on 22 working days gives you 550 a month, which is small for most campaigns.

Are pre-warmed inboxes worth it?

They cost more per mailbox and still need warm-up to keep running while you send. Check whether you own the domain and can export the mailbox before paying a premium for one.

Sources

Checked September 2026:

• Instantly pricing: account prices; Growth $47, Hypergrowth $97 (125,000 emails), Outreach add-on $87; API on all plans.

• Instantly DFY help article: 5 accounts per domain, domain ownership, platform-only use, cancellation.

• SmartSenders pricing: $4.50 and $3.99 mailboxes, mailboxes per domain, 75-mailbox minimum.

• SmartSenders FAQ: no transfer or use outside Smartlead.

• Smartlead pricing: Pro plan $94 (90,000 sends), API and webhooks; the 240,000-send step at $228 is from its plan slider.

• Maildoso pricing: 30 mailboxes for $75, 15 cold emails a day, mailboxes per domain, domain transfer, money-back guarantee, deleting and recreating mailboxes, CSV export, API.

• Zapmail: plans, pre-warmed mailboxes, domain ownership, no refunds, integrations, API on Pro.

• Mailforge pricing and Mailforge: 10-slot minimum, slots, domain transfers, works with any sending software.

• Premium Inboxes: $3.50 per inbox including domains, no contracts, 15-a-day note, replacement inboxes, client API.

• InboxKit pricing: $3.00 monthly, no minimum, warm-up add-on, integrations, API.

• InboxKit refund policy: cancellation and refunds.

Compare the full cost, then start with 12 mailboxes and everything included.

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