TL;DR
- Cheapest per mailbox: Maildoso scales from $2.50 to $0.49 per mailbox, but it runs its own SMTP infrastructure, not Google or Microsoft.
- Native Google/Microsoft, no minimum: InboxKit lists $3 monthly or $2.50 annual per mailbox with no minimum.
- Most isolated: Infraforge at $4 per mailbox on dedicated servers, with a dedicated IP at $99/month.
- Direct from Google: Workspace Business Starter lists at $7.00 per user per month on an annual commitment, and you handle domains and DNS yourself.
- Volume rule: stay near 30 sends per mailbox per day and under 0.30% spam rate regardless of vendor.
Before you launch a cold email campaign you need domains and mailboxes, and that choice shapes cost, deliverability and how much admin work you take on. A growing group of vendors sell this as a managed layer that plugs into Smartlead or Instantly. This guide compares the main options on the numbers that matter.
Pricing was read from each vendor's pricing page in October 2026 and can change; vendor-stated volume limits and secondary-sourced claims are marked (directional). Confirm current terms before you buy.
The Short Answer
There is no single best provider. Pick by what you are optimising for: lowest cost per mailbox (Maildoso, Mailforge), native Google or Microsoft inboxes with flexible sizing (InboxKit, Zapmail), isolation (Infraforge), or minimal vendor risk (buying direct from Google or Microsoft). Whichever you choose, deliverability still depends on authentication, volume discipline and list quality.
Provider Comparison at a Glance
| Provider | Per mailbox / mo | Minimum | Mailbox type | Domains | Dedicated IP |
|---|---|---|---|---|---|
| Mailforge | $3 | 10 | Shared-IP SMTP | Buy in-app (.com about $14/yr) | No |
| Infraforge | $4 | 10 | Private mailboxes, dedicated servers | Buy in-app (.com about $14/yr) | $99/IP/mo |
| Maildoso | $2.50 down to $0.49 by plan size | 30 on the smallest plan | Proprietary SMTP, rotating IPs | Bundled on quarterly plans only | No (rotating) |
| InboxKit | $3 monthly / $2.50 annual | None | Google, Microsoft or Azure | Pre-warmed domains from $12.50 one-time | Not stated |
| Zapmail | $2.99 to $3.90 by plan | 10 (Starter) | Google or Microsoft | Not stated | Not stated |
| Google Workspace (direct) | $7.00 (annual list) | 1 | Native Google | Bring your own | No |
We did not verify Microsoft 365 direct pricing, so it is left out of the table rather than guessed. See our Google Workspace vs Microsoft 365 for cold email comparison for that decision.
Sending Limits, DNS and Sequencer Support
| Provider | Recommended daily volume | Auto DNS | Smartlead / Instantly |
|---|---|---|---|
| Mailforge | 30 per mailbox (max 100), 2 to 3 mailboxes per domain | Yes (SPF, DKIM, DMARC) | Not stated on pricing page |
| Infraforge | 30 per mailbox (max 100), 2 to 3 mailboxes per domain | Yes, editable | Not stated on pricing page |
| Maildoso | Up to 15 cold sends per mailbox; 8 or fewer mailboxes per domain recommended | Via API | Not confirmed |
| InboxKit | Not stated | Yes, on every mailbox | Yes, names Instantly and SmartLead |
| Zapmail | Not stated | DNS management and health checks | Not named |
Only InboxKit's page confirmed Smartlead and Instantly support by name. For the others, test the connection on a trial before you buy a full set of mailboxes.
Provider Notes
Mailforge
$3 per mailbox slot per month, 10-slot minimum, monthly or yearly billing (yearly shows two months free), no contract. Mailboxes sit on a shared IP pool. SPF, DKIM and DMARC are automated. Domain masking is $2 per domain per month. You pay for every purchased slot whether active or not.
Infraforge
$4 per slot with quarterly or yearly billing and a 10-slot minimum. Mailboxes are private, on dedicated servers, and a dedicated IP costs $99 per IP per month. The optional Masterbox adds a unified inbox view for $7 to $9 per workspace per month. DNS is automatic but editable.
Maildoso
Monthly plans scale from 30 mailboxes at $2.50 each ($75/mo) to 300 at $0.75 ($225/mo) and 1,000 at $0.49 ($499/mo). It runs proprietary SMTP infrastructure with rotating IPs, so these are not Google or Microsoft accounts. The vendor notes reduced inbox placement is possible when targeting Gmail or Yahoo addresses and recommends at least 14 days of warm-up. Domains transfer back at no charge if you cancel.
InboxKit
$3 per mailbox monthly or $2.50 annual, no plans, no base fee and no minimum. Mailboxes are Google Workspace or Microsoft 365 at the same price, and Azure-based mailboxes are $30 per tenant per month. The page itself shows both $2.50 and $3.00 figures, so check the checkout total.
Zapmail
Starter is $39 for 10 mailboxes, Growth $99 for 30, and Pro $299 for 100 on monthly billing, covering Google and Microsoft mailboxes. API access is Pro only. Google Workspace mailboxes move to updated pricing after the first year.
Google Workspace direct
Business Starter lists at $7.00 per user per month on an annual commitment. You buy domains and configure DNS yourself. It costs more per mailbox than the managed providers, but you hold the account directly.
Risk: Shared Infrastructure and Resold Seats
Know what you are renting. Shared or rotating IPs (Mailforge, Maildoso) mean other customers' behaviour can affect your reputation. For Google or Microsoft mailboxes sold by third parties, whether seats are resold or direct is not stated on InboxKit's or Zapmail's pricing pages. We found no primary Google text on resold seats used for outbound, so check your contract and Google's terms.
Google's bulk-sender rules apply no matter where the mailbox comes from: spam rate under 0.30%, valid authentication, and one-click unsubscribe above 5,000 messages per day. Cold email is not named as banned on that page, but complaint rates are what get accounts throttled. Read our SPF, DKIM and DMARC setup guide and deliverability monitoring guide.
How to Choose
- Want native Google/Microsoft inboxes and a flexible start? Shortlist InboxKit or Zapmail.
- Want the lowest cost and accept non-Google infrastructure? Look at Mailforge or Maildoso.
- Want isolation and will pay for it? Infraforge, plus a dedicated IP if volume justifies $99/month.
- Want the lowest account-ownership risk? Buy direct and run domains and DNS yourself.
- Using Smartlead or Instantly? Confirm the integration on a trial. See Smartlead vs Instantly.
Budget example (25 mailboxes, vendor list prices): Mailforge $75/mo monthly or $60/mo yearly; Infraforge $83/mo yearly or $100/mo quarterly, before domains and any dedicated IP. Plan for warm-up too: see warm-up tools.
Mailboxes are only the base layer. Domain count, rotation and monitoring matter as much; our cold email infrastructure guide and domain and mailbox rotation guide cover the rest.
Frequently Asked Questions
Is Mailforge or Infraforge better for cold email?
Mailforge is $3 per mailbox slot on a shared IP pool. Infraforge is $4 per slot on dedicated servers, and a dedicated IP is $99 per month extra. If you want isolation from other senders, Infraforge is the closer fit; if cost per mailbox matters most, Mailforge is cheaper.
Do I need to buy domains separately?
On Mailforge and Infraforge, yes: you buy them in-app, with .com shown at about $14 per year. Maildoso bundles domains only on its quarterly plans. Zapmail's pricing page does not state domain terms, so confirm before you commit.
Is there a minimum number of mailboxes?
Mailforge and Infraforge sell a minimum of 10 slots, Maildoso's smallest standard plan is 30, Zapmail's Starter plan is 10, and InboxKit lists no minimum. You pay for every purchased slot on Mailforge and Infraforge whether or not it is active.
What authentication does Google require for senders?
All senders need SPF or DKIM, valid forward and reverse DNS, TLS, and a spam rate under 0.30% (Google recommends under 0.10%). Senders above 5,000 messages per day to Gmail also need SPF, DKIM and DMARC, From-domain alignment, and one-click unsubscribe. See our sender requirements guide.
Are reseller Google or Microsoft mailboxes against the providers' terms?
One competitor blog (directional) claims reseller accounts raise suspension risk, but we found no primary Google text confirming it. Whether InboxKit and Zapmail sell resold or direct seats is not stated on their pages. Check the provider's contract and Google's Workspace terms before you scale.
How many cold emails can one mailbox send per day?
Mailforge and Infraforge recommend about 30 per mailbox per day with a hard maximum of 100, and 2 to 3 mailboxes per domain. Maildoso says up to 15 cold sends per mailbox per day. Treat these as vendor guidance, and see how many domains and mailboxes you need.
Want the infrastructure, list building and sequences handled for you? Start with our infrastructure guide or talk to our team.
By the GenFlows GTM engineering team. Pricing read from vendor pages; verify before purchase. Last updated October 2026.
The GenFlows team builds AI-powered cold outbound systems for B2B teams.