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InboxKit or Maildoso: Which One Should You Pick?
Here's how InboxKit and Maildoso stack up on price, the mailbox types each one supports, deliverability tooling, and how well they plug into cold email platforms such as Sendbox.
InboxKit and Maildoso are independent third-party mailbox providers, neither is a Sendbox product. This comparison is based on each provider's publicly listed pricing and features.
The verdict
InboxKit pulls ahead on flexibility across tiers and how much comes bundled in. Three tiers are on offer, Professional at $31 for 10 mailbox slots, Agency at $81 for 30, Enterprise at $250 for 100, with the per-mailbox rate sliding from $3.10 down to $2.50 as you move up. Placement testing, an email verifier, a blacklist checker, and DNS automation ship with every tier, while Email Warmup sits outside as a $3-per-mailbox add-on no matter which tier you're on.
Maildoso's edge is straightforward price: $1.90 per SMTP mailbox to start, backed by the strongest scale record in the category at 400,000+ mailboxes and 10 million-plus emails sent daily. Go with InboxKit if you want GWS, M365, and Azure flexibility with most of the deliverability stack already built in. Go with Maildoso if the cheapest SMTP mailboxes matter most and you're fine routing warmup through Sendbox or another sending tool.
Scoreboard
Which provider has the edge on each of the 12 rows in the table below.
A count of rows, not a weighted score, read the verdict for which differences matter most.
Feature comparison
InboxKit vs Maildoso, row by row
| Feature |  InboxKit |  Maildoso |
|---|---|---|
| Price per MailboxPricing | $3.10-$2.50 by tier Three tiers to choose from: Professional at $31/mo for 10 slots ($3.10 each), Agency at $81/mo for 30 slots ($2.70 each), Enterprise at $250/mo for 100 slots ($2.50 each). Warmup adds $3 per mailbox on top. | $1.90-$2.50/mo Edge Pure SMTP starts at $1.90; the SMTP-plus-Google-Workspace Combo option runs $2-$3/mo. |
| Mailbox TypesInfrastructure | GWS + M365 + Azure Edge All three of Google Workspace, Microsoft 365, and Azure are on the table. | SMTP + Combo Choose plain SMTP or the Combo tier that layers in Google Workspace. |
| IP LocationInfrastructure | US IPs Edge Every mailbox sends from a US-based IP. | Not specified Where the IP is located depends on which mailbox type you pick. |
| Inbox Placement RateDeliverability | 95% claimed Edge Claims a 95 percent placement rate across every mailbox type it offers. | Not published Doesn't publish a placement-rate figure. |
| DNS AutomationInfrastructure | Full auto SPF, DKIM, DMARC, and MX all configure themselves. | Auto DNS DNS configuration is automated out of the box. |
| Built-in WarmupDeliverability | Yes (add-on) Edge A native warmup tool, billed as a $3/mailbox monthly add-on. | No You'll need to source warmup from your sending tool instead. |
| Inbox Placement TestingDeliverability | Yes Edge Lets you check whether a send actually lands in the inbox or the spam folder. | No Not offered, route this through your sending platform instead. |
| Email VerifierDeliverability | Yes Edge Verification is built directly into the platform. | No No native verifier is offered. |
| Blacklist CheckerDeliverability | Yes Edge Keeps an eye on IPs and domains against known blacklists. | No Not built in natively. |
| Scale Track RecordScale | Enterprise clients Counts 11x, Zendesk, PwC, and Merck among its customers. | 400K+ mailboxes Edge Runs 400,000-plus mailboxes and pushes over 10 million emails a day. |
| G2 RatingSocial Proof | Not listed No G2 rating on record. | 4.7 (159 reviews) Edge Sits at 4.7 out of 5 across 159 verified G2 reviews. |
| API AccessAutomation | Yes API access supports automated mailbox provisioning. | Yes + MCP Offers both API and MCP support for automation. |
On this page8
Infrastructure and Mailbox Types
Mailbox variety is where these two diverge most. InboxKit houses Google Workspace, Microsoft 365, and Azure mailboxes under a single account, which means you can experiment to see which provider actually delivers best for a given domain and audience. Maildoso, by contrast, is built around SMTP, with a Combo tier available if you want Google Workspace layered on top.
Google Workspace mailboxes tend to land in the inbox more reliably than SMTP for cold outreach, and InboxKit hands you that option from the first mailbox you provision. Maildoso makes up the difference with a lower price and a scale record to match, 400,000-plus mailboxes under management and over 10 million emails processed daily.
Key takeaways
- InboxKit runs GWS, M365, and Azure from one account
- Maildoso: SMTP starting at $1.90, Combo (SMTP+GW) at $2-$3
- InboxKit sticks to US-based IPs; Maildoso's location depends on mailbox type
- Maildoso holds the bigger scale record at 400K+ mailboxes managed
Deliverability Tools
InboxKit folds an entire deliverability toolkit into its infrastructure layer, warmup, placement testing, verification, blacklist monitoring, all of it. That's not typical; most competitors, Maildoso included, push deliverability responsibility onto whatever sending tool you use. Maildoso genuinely ships none of those: no warmup, no verifier, no placement testing.
You'll be sourcing all of it from Sendbox or a comparable platform. Teams already running Sendbox (which covers each of those bases) won't notice the gap. Teams that specifically want deliverability monitoring living at the infrastructure level, though, have only one real option here, and it's InboxKit.
Key takeaways
- InboxKit ships placement testing, a verifier, and a blacklist checker natively, plus warmup as a $3/mailbox add-on
- Maildoso includes none of that deliverability tooling
- Sendbox fills the warmup and monitoring gap regardless of which provider you're on
InboxKit vs Maildoso: Cost at 100+ Mailboxes
Line up 100 mailboxes on each and InboxKit's Enterprise tier lands at $250/mo flat (the included 100-slot rate of $2.50 apiece). Maildoso's SMTP fleet runs $190 to $250/mo at that same count, and the Combo tier with Google Workspace pushes it to $200-$300/mo. At 100 mailboxes, the base bills are genuinely close.
Two things belong in the real math, though: InboxKit's Email Warmup is a separate $3-per-mailbox add-on (another $300/mo at this scale), but it also throws in the verifier, placement testing, and blacklist checker that Maildoso doesn't offer at any price. And at smaller counts, the 10 to 30 mailbox range, InboxKit's Professional and Agency tiers charge $3.10 and $2.70 per mailbox respectively, not the $2.50 headline rate, so plan your budget around the tier you'll actually land in.
Key takeaways
- At 100 mailboxes: InboxKit runs $250/mo against Maildoso SMTP's $190-$250/mo
- Deliverability tooling ships with InboxKit and not with Maildoso
- Past 200 mailboxes, the price gap widens in Maildoso's favor
InboxKit vs Maildoso: Which One Fits Your Use Case
InboxKit makes sense if you'd rather have one provider handle mailbox provisioning, DNS, and the full monitoring stack, verifier, placement testing, blacklist checker, right out of the base tier. Rates run $3.10 on Professional, $2.70 on Agency, and $2.50 on Enterprise, with Warmup priced separately at $3 per mailbox. It also wins on mailbox variety, spanning Google Workspace, Microsoft 365, and Azure.
Maildoso is the better call if raw per-mailbox cost is what matters most and you're already running Sendbox or another platform that handles warmup for you. Its 400,000+ mailbox track record and category-leading G2 reviews back up the price. Either way, both connect into Sendbox for campaign management, sequencing, and AI warmup.
Key takeaways
- InboxKit fits teams that want one provider to cover everything
- Maildoso fits teams chasing the cheapest mailboxes while Sendbox covers deliverability
- Both plug into Sendbox for sending and campaign management
Strengths and limitations
Pros & cons
Strengths6
- Google Workspace, Microsoft 365, and Azure mailboxes all live in one platform
- Placement testing, an email verifier, and a blacklist checker ship natively, with warmup as a $3/mailbox add-on
- US-based IPs backing a claimed 95 percent placement rate
- Each domain has its own monitoring panel
- DNS (SPF, DKIM, DMARC, MX) configures automatically
- Connects to 24-plus tools, Sendbox included
Limitations3
- Costs more per mailbox than Maildoso SMTP ($2.50 vs $1.90)
- Has no G2 rating or visible review count
- A relatively newer name in infrastructure
Strengths5
- The lowest per-mailbox starting price at $1.90/mo
- A proven scale record: 400K+ mailboxes, 10M+ emails daily
- 4.7 stars on G2 across 159 verified reviews
- API and MCP support both available for automation
- Domains priced from $2 each
Limitations3
- No native warmup, verification, or placement testing
- Base tier is SMTP-only; Google Workspace requires the Combo upgrade
- Deliverability tooling has to come from your sending platform
Using either provider with Sendbox
Both providers connect to Sendbox through a one-click, API-key-based import. Once connected, Sendbox takes over AI warmup, sequencing, deliverability monitoring, and campaign management on top of either provider's mailboxes. You also have the option of skipping a separate provider entirely and buying mailboxes straight through Sendbox. And if you're coming from Instantly, Smartlead, or EmailBison, Sendbox pulls your campaigns and leads across automatically via API key.
- Mailboxes can be provisioned right inside Sendbox, no manual setup, live in about 30 minutes
- Every plan runs on dedicated IPs with isolated infrastructure
- Plays nicely with any of the infrastructure providers above (InboxKit, Maildoso, Zapmail, Mailforge)
- Migrating from Instantly, Smartlead, or EmailBison takes an API key, not a rebuild
- A 350M+ lead database comes with the platform
- Dialer, CRM, and AI reply tagging are built in rather than bolted on
- Pricing is not per seat
It depends what you're optimizing for. InboxKit is the more complete package, Google Workspace, Microsoft 365, and deliverability tools built in. Maildoso wins on per-mailbox price and has the stronger scale history. If Sendbox is already handling your warmup and monitoring, Maildoso tends to be the better value; if you'd rather one provider cover everything, InboxKit is the pick.
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