Inboxkit
Inbox infraAPI-first domains and cold inboxes across Google, Microsoft, and Azure, with monitoring. DIY, not done-for-you.
The verdict
Inboxkit is API-first domains and cold inboxes for bulk provision without living in a dashboard. Google and Microsoft are $2.50 per mailbox per month on annual. Monthly is $3.00. Azure is $30 per tenant per month for up to 100 mailboxes. Warmup add-on is $3 per mailbox. There is no volume tier discount on the mailbox sticker. Discount equals billing cycle. The trade is sharp DNS edges.
Some records on your main domain can get dropped. Forwarding defaults surprise you. Script setup and verify records after. Lucero's large grid saw inbox brands land close on human reply, so the brand name will not decide where mail lands. Hand send to Smartlead for agency fleets. Premium Inboxes when Slack-human done-for-you wins. Zapmail when pre-warmed year-one speed wins. Skip Instantly done-for-you mailboxes if you plan to scale.
Best for
Operators and GTM engineers who want programmable inbox and domain provisioning, Azure or Entra density, InfraGuard-style monitoring, and flat per-mailbox math without done-for-you rates.
Not for
Skip if you will not own post-provision DNS QA. Skip if unlimited human replacements are the product you are buying. Skip if you only need five pre-warmed boxes this week and will not script anything.
Pricing truth
Wallet model from Inboxkit pricing (checked 2026-09-24). Google Workspace and Microsoft 365 are $2.50 per mailbox per month on annual. Monthly is $3.00. Quarterly lands near $2.70. Azure is $30 per tenant per month for up to 100 mailboxes. Warmup add-on is $3 per mailbox per month. InfraGuard monitoring often frames the first month free. Flat scale: no volume tier discount on the mailbox sticker. Discount is billing cycle, not seat ladders. Rough monthly cost: 100 mailboxes on annual is about $250 per month before warmup and Azure. Two Azure tenants add about $60. Contrast Premium Inboxes Insured at $4.50 done-for-you and Zapmail year-two Growth cliff when you graduate. The brand name alone will not decide where your mail lands.
When we use it
- Script domains and inboxes in bulk through the API (a way for your own code to control the tool) instead of clicking a dashboard.
- Use Azure tenants (a Microsoft account space you control) when per-mailbox Microsoft pricing hurts.
- Run DIY infra into your sequencer (tool that sends email steps over days) without paying done-for-you service fees.
- Monitor secondary domains when you are operating at hundreds to thousands of seats.
How to wire it
- Provision domains and mailboxes through the API. Treat the dashboard as a fallback, not the production path.
- Verify DNS after every batch. Do not trust silent defaults.
- Check the DNS records on your main domain after setup. Domain forwarding is often on by default, so turn it off if you do not want it.
- Add Azure tenants only when Microsoft density is the job. Budget about $30 per tenant for up to 100 mailboxes.
- Connect your sequencer. Warmup is an add-on near $3 per mailbox if you need it.
Margin notes
- Annual floor is $2.50 per mailbox for Google and Microsoft. Monthly is $3.00.
- Azure is $30 per tenant per month for up to 100 mailboxes. Two tenants at 100 boxes sketch to about $250 plus $60 before warmup.
- Warmup add-on is $3 per mailbox. InfraGuard often frames month one free.
- No volume tier discount on the sticker. Pay cycle discount instead.
- The API is the product. DNS QA after provision is your job.
FAQ
Inboxkit vs Zapmail. API vs pre-warmed?▾
Inboxkit wins API bulk provision, Azure tenants, and monitoring. Zapmail wins already-warmed minutes-to-live. Same mailbox class. Opposite ops. Model Zapmail year two before you lock volume.
Do I need Azure tenants?▾
Only if cheap Microsoft density on Azure or Entra is the job. Each tenant is about $30 per month for up to 100 mailboxes. Skip Azure if Google Workspace seats already cover you.
What does $2.50 annual actually include?▾
The Google or Microsoft mailbox sticker on annual billing. Warmup is extra near $3. Azure is extra near $30 per tenant. DNS QA is your time. Flat sticker. No volume tier discount.
When do I graduate to Premium Inboxes?▾
When Slack-human done-for-you and unlimited replacements matter more than API control. When fixing DNS by hand becomes the weekly cost. When non-technical ops owns the fleet.
Should I buy Instantly done-for-you instead?▾
No if you plan to scale. Buy boxes from Inboxkit. Send on Smartlead for agency fleets. Instantly is fine for one founder running their own campaigns.
Does Inboxkit win deliverability by logo?▾
No. Lucero's large grid saw brands cluster close on human reply. Fix list, offer, copy, and hygiene. Buy Inboxkit for API and Azure ops.
What should I do next?▾
Script a small domain batch. Verify DNS. Connect into Smartlead. A/B against Premium Inboxes or Zapmail on the same list before you lock annual.
Next step
If you need running inboxes from your own code, Azure tenants, and flat per-mailbox math, open Inboxkit. If you need Slack-human done-for-you, open Premium Inboxes. If you need pre-warmed year-one speed, open Zapmail and model year two. Buy boxes here. Send on Smartlead. Try Inboxkit Try Premium Inboxes Try Zapmail Try Smartlead