InboxKit Pricing 2026: Three Tiers and How They Actually Scale
InboxKit ships three published tiers (Professional, Agency, Enterprise) with per-mailbox rate dropping as tier rises. Plus $3/mailbox Email Warmup as an add-on. Here is how the bill actually assembles.
Bottom line
InboxKit publishes three tiers on annual billing: Professional at $31/mo includes 10 mailbox slots (additional at $3.10 each), Agency at $81/mo includes 30 mailbox slots (additional at $2.70 each), and Enterprise at $250/mo includes 100 mailbox slots (additional at $2.50 each). The effective per-mailbox cost drops from $3.10 at the Professional tier to $2.50 at the Enterprise tier, so the $2.50 figure that gets quoted in shorthand is the Enterprise-tier rate, not a universal price. The base tiers include automated DNS, the official admin panel with 2FA, app passwords, 24+ sequencer integrations, inbox placement testing, an email verifier, a blacklist checker, real-time monitoring, unlimited team members, full API access, and US IPs.
Email Warmup is a separate add-on at $3/mailbox/month across all tiers; Azure tenants are $30 per domain; the InfraGuard protection suite is a paid add-on (first month free). Volume discounts are available for fleets above 500 mailboxes via custom pricing. The structural advantage: every tier supports Google Workspace, Microsoft 365, and Azure mailboxes under one provider, so a mixed-provider fleet does not pay a switching premium.
InboxKit Plans
| Plan | Price | What you get | Watch out for |
|---|---|---|---|
| Professional annual billing, 10 mailbox slots included | $31/mo |
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| Agency annual billing, 30 mailbox slots included (Most Popular) | $81/mo |
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| Enterprise annual billing, 100 mailbox slots included | $250/mo |
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InboxKit bill at common configurations (annual billing assumed)
| Usage scenario | Monthly cost | Notes |
|---|---|---|
| Solo operator, 5 mailboxes, no warmup | $31/mo | Professional tier covers 10 slots so you have headroom. Effective per-mailbox: $6.20 because you are under the included count. The base fee dominates at this scale. |
| Solo operator, 10 mailboxes, no warmup | $31/mo | Hits the Professional slot ceiling exactly. Effective rate drops to $3.10/mailbox. The optimal point on the Professional tier. |
| Solo operator, 10 mailboxes with warmup | $61/mo | $31 Professional base + $30 warmup add-on (10 x $3). Real bill once warmup is included; most serious operators add this. |
| Small team, 30 mailboxes with warmup | $171/mo | $81 Agency base + $90 warmup add-on. The sweet spot of the Agency tier. Effective all-in cost: $5.70/mailbox. |
| Growth team, 50 mailboxes with warmup | $285/mo | $81 Agency base + 20 x $2.70 (extra mailboxes) + 50 x $3 warmup = $81 + $54 + $150. Per-mailbox: $5.70 all-in. |
| Enterprise team, 100 mailboxes with warmup | $550/mo | $250 Enterprise base + $300 warmup add-on (100 x $3). Per-mailbox all-in: $5.50. The economics improve relative to lower tiers. |
| 300 mailboxes with warmup | $1,650/mo | $250 base + 200 x $2.50 extra mailboxes + 300 x $3 warmup = $250 + $500 + $900. Per-mailbox all-in: $5.50. |
| 500+ mailboxes | Custom pricing | Volume discount conversation kicks in at this fleet size. Sticker math (300 x extras + warmup) is not the assumed final price; expect negotiation. |
How the three-tier structure actually shapes the bill
InboxKit's pricing has three breakpoints that matter for cost modeling. Professional at $31/mo covers up to 10 mailbox slots with extra mailboxes at $3.10 each. Agency at $81/mo covers up to 30 mailbox slots with extras at $2.70 each.
Enterprise at $250/mo covers up to 100 mailbox slots with extras at $2.50 each. The practical implication: each tier has a "sweet spot" where you hit the included slot count exactly. Hit the sweet spot on Professional (10 mailboxes) and your effective rate is $3.10.
Hit the sweet spot on Agency (30 mailboxes) and the effective rate drops to $2.70. Hit the sweet spot on Enterprise (100 mailboxes) and you land at $2.50. Going under the sweet spot wastes the included slots.
Going over the sweet spot triggers the per-extra-mailbox rate that, while still tier-priced, does not bring the bill down further. Plan your tier against the mailbox count you actually intend to run, not the count you might grow to. The path to lower per-mailbox cost is climbing to the next tier, not stretching the current one.
Key takeaways
- Professional ($31): 10 mailboxes included, $3.10 per extra
- Agency ($81): 30 mailboxes included, $2.70 per extra
- Enterprise ($250): 100 mailboxes included, $2.50 per extra
- Effective per-mailbox cost drops only when you climb tiers, not within them
Why warmup is the $3/mailbox line most evaluators miss
The InboxKit pricing page lists Email Warmup as an explicit add-on at $3 per mailbox per month, applied across all three tiers. This is the single most-misunderstood line in the pricing surface because warmup is generally treated as table-stakes infrastructure for cold email rather than an optional service. The math: a 30-mailbox Agency fleet without warmup is $81/mo.
The same fleet with warmup is $171/mo. A 100-mailbox Enterprise fleet without warmup is $250/mo; with warmup it is $550/mo. The warmup line item often equals or exceeds the base subscription cost.
The practical implication: budget warmup into your baseline rather than treating it as an upgrade. Two scenarios where you can defer or skip the InboxKit warmup add-on: first, if your sending platform (SendKit, Instantly, Smartlead) already runs native warmup, you can route warmup traffic through that platform and save the InboxKit add-on cost. Second, if you are running only inbound or transactional traffic, warmup may not be necessary at all.
For pure cold email workflows, plan for the add-on.
Key takeaways
- Email Warmup is a $3/mailbox/mo add-on, NOT bundled into base tiers
- On a 30-mailbox fleet, warmup adds $90/mo on top of the $81 Agency base
- On a 100-mailbox fleet, warmup adds $300/mo on top of the $250 Enterprise base
- Native warmup from your sending platform can substitute for the InboxKit add-on
Provider-mixing economics across the three tiers
A real differentiator on InboxKit is that every tier supports Google Workspace, Microsoft 365, and Azure mailboxes under the same provider. The choice of mailbox type does not change the tier rate. A 30-mailbox Agency fleet running 50 percent GWS and 50 percent M365 costs the same $81/mo as a fleet running 100 percent GWS.
This matters because cold email deliverability has shifted toward provider-mixing strategies over the last two years. Running 60 percent GWS alongside 40 percent M365 spreads reputation risk across two distinct ESP infrastructures. Specialized providers (Zapmail GWS-only, Mailforge SMTP-only) force mixed-provider fleets to live across multiple vendor accounts with separate billing, separate DNS flows, and separate panel logins.
On InboxKit, the mixed fleet lives on one bill and one panel. The exception: Azure tenants carry a $30-per-domain fee on top of the tier economics. GWS and M365 do not trigger that fee.
For teams running pure Azure, factor the per-domain charge into the budget.
Key takeaways
- GWS, M365, and Azure all supported at the same tier rate
- Mixed-provider fleets pay one bill, manage one panel
- Azure tenants add $30/domain on top of tier economics
- Provider-mixing avoids ESP reputation concentration risk
Which buyer profile fits which tier
Professional ($31/mo) fits solo operators and very small teams running fewer than 12 mailboxes. The included 10 slots is the sweet spot; above 12 mailboxes the per-extra-mailbox rate makes Agency cheaper on the all-in math. Agency ($81/mo) fits small agencies and SDR teams running 15-40 mailboxes.
The 30 included slots cover the typical reputation-diversification fleet for a 3-6 person outbound team. This is the tier most growth-stage outbound functions land on. Enterprise ($250/mo) fits established agencies, enterprise outbound teams, and high-volume cold email operations running 75-150 mailboxes.
The 100 included slots fit most enterprise-scale fleets without needing to add many extras. Volume discounts above 500 mailboxes are negotiated separately; teams approaching that fleet size should plan a sales conversation rather than assuming the published $2.50 extra-mailbox rate holds at scale.
Key takeaways
- Professional: solo operators, under 12 mailboxes
- Agency: small agencies and 3-6 person SDR teams, 15-40 mailboxes
- Enterprise: established agencies and enterprise outbound, 75-150 mailboxes
- 500+ mailboxes: custom pricing conversation expected
Keep reading
Got questions? We've got answers.
Only at the Enterprise tier. The published pricing has three tiers: Professional at $31/mo (10 mailbox slots, $3.10 per extra), Agency at $81/mo (30 slots, $2.70 per extra), and Enterprise at $250/mo (100 slots, $2.50 per extra). The "$2.50" quote refers specifically to the Enterprise tier extras rate. Professional buyers pay $3.10/mailbox; Agency buyers pay $2.70/mailbox.
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