I’d choose Frostmailer for Microsoft Outlook inboxes and Maildoso for SMTP-based sending. Before buying, check mailbox access, domain ownership, and sending limits. SMTP access alone does not prove Microsoft hosting.
The price per inbox tells only part of the story. Frostmailer tenants send about 200 emails per day in total, which is 2 to 3 per inbox at 100 inboxes per tenant or about 4 at the recommended 50. I’d compare cost against planned sending volume, not just mailbox count.
Quick Comparison
| What I’d compare | Frostmailer | Maildoso |
|---|---|---|
| Hosting and access | Microsoft Azure/Outlook inboxes; no standalone SMTP plans | SMTP mailboxes only |
| Sending tools | EmailBison, Smartlead, PlusVibe, Instantly, Success.ai, MasterInbox | Not verified; check Maildoso's documentation |
| Setup and warm-up | About 24-hour setup; warm-up included; pre-warmed options | About 15-minute setup; at least 14 days of warm-up |
| Price | €30/month per standard tenant or €50 pre-warmed | $225/month for 300 mailboxes, plus domains on monthly plans |
| Domain ownership | One .com domain included per Azure tenant | $15/year per domain on monthly plans |
| Scaling and handoff | Tenant-based; confirm admin rights | SMTP credentials; confirm DNS and transfer access |
| Automation | REST API and MCP | API on every plan; no MCP |
My bottom line: check what you control before comparing price. Include sequencer fees, domain costs, reply handling, and cancellation terms in your budget. Neither mailbox type guarantees inbox placement.
i compared 21 cold email infrastructure tools (18 of them are trash)
Frostmailer vs. Maildoso: Hosting and Mailbox Access
Frostmailer provides native Microsoft-hosted inboxes, while Maildoso documents SMTP/IMAP mailbox access. The differences affect inbox access, DNS control, and warm-up.
| Provider | Capability | Source | Verification status |
|---|---|---|---|
| Frostmailer | Microsoft Azure/Outlook mailbox hosting | Verified | |
| Frostmailer | Standalone SMTP mailboxes | Unavailable | |
| Maildoso | SMTP mailboxes | Documented |
Frostmailer’s Azure and Outlook Mailboxes
Frostmailer’s Microsoft hosting gives teams Outlook-style inbox access, not just SMTP credentials. Agencies can manage inboxes directly alongside their sending workflow.
Maildoso’s Hosting and Access Options
Maildoso’s current purchase docs describe new mailbox purchases as SMTP mailboxes.
This setup supports sending-tool workflows, but not native Outlook-style inbox management. Maildoso does not document native Microsoft mailbox provisioning for these plans.
Domain Setup, DNS, and Warm-Up
Frostmailer configures SPF, DKIM, and DMARC on its Azure tenants. Check how Maildoso handles DNS and tracking domains before buying.
Frostmailer’s standard setup includes warm-up. Its pre-warmed tenants have 4 weeks of warm-up done before delivery. Maildoso warm-up is self-run, for at least 14 days.
Domain ownership matters for client handoffs, too. Frostmailer includes one .com domain per Azure tenant. Maildoso charges $15 per domain per year on monthly plans. Check the transfer terms before registering client domains.
Agency Setup and Client Handoffs
Once mailbox hosting is settled, check how each system connects to your sending stack and who controls the client handoff.
Connecting to Sending Platforms
Frostmailer connects to EmailBison, Smartlead, Instantly, PlusVibe, Success.ai, and MasterInbox. Check Maildoso's documentation for its supported sending tools.
| Agency need | Frostmailer | Maildoso |
|---|---|---|
| Auth method | Microsoft OAuth for Azure/Outlook | SMTP credentials for SMTP plans |
| Send/reply path | Microsoft inbox access through OAuth | Sends through SMTP and syncs replies through IMAP |
| Setup fields | OAuth authorization | Host, port, username, and password |
| Provisioning | App, REST API, and MCP server | Dashboard and API; no MCP server |
| Account organization | Azure tenants with 25, 50, or 100 inboxes | Smallest plan 30 mailboxes |
The next check is whether the client can take over access, credentials, and admin control.
Client Permissions, Provisioning, and Scaling
Receiving credentials doesn't mean the client is ready to send. Frostmailer says Azure setups are typically live in about 24 hours. Maildoso advertises roughly 15-minute SMTP setup. Frostmailer’s Build and Release service hands over the outbound system after 14 days. Setup speed and ownership are separate questions.
Before a handoff, confirm who gets mailbox access, who controls tenant settings, and who can change DNS or revoke credentials. Microsoft inbox handoffs depend on tenant/admin permissions. SMTP plans use exported credentials. Do not assume Azure tenants include full admin rights. Maildoso provides SMTP credentials for upload to a sequencer.
Frostmailer offers a REST API and MCP server for automated provisioning, and Maildoso offers an API on every plan but no MCP server. Check permission scopes and what happens when credentials are replaced before standardizing onboarding.
Pricing and Sending Capacity
Tenant Prices and Total Agency Costs
After access and handoff, compare cost per usable inbox and daily sending volume. The advertised account price doesn't tell you the full cost: Frostmailer bills per tenant, while Maildoso prices its SMTP plans by mailbox count.
| Cost or condition | Frostmailer Azure Standard | Frostmailer Azure Pre-warmed | Maildoso SMTP plans |
|---|---|---|---|
| Price and billing | €30 per tenant per month | €50 per tenant per month | $75.00/month for 30 mailboxes; $225.00/month for 300; $499.00/month for 1,000 |
| Mailboxes | 25, 50, or 100 per tenant; 50 recommended | 25, 50, or 100 per tenant | 30, 300, or 1,000 |
| Domains | One .com domain included per tenant | One .com domain included per tenant | $15.00 per year per domain on monthly plans |
| Sending guidance | About 200 emails per tenant per day (2 to 3 per inbox at 100, about 4 at 50) | About 200 emails per tenant per day | Not verified |
| Minimum purchase | One tenant | Two tenants | Smallest plan 30 mailboxes |
| Exclusions | Sending-platform subscription separate | Sending-platform subscription separate | Sequencer separate; monthly plans add domain costs |
Sources: Frostmailer pricing and product details. Maildoso pricing and sending documentation.
With 100 accounts per tenant, Frostmailer costs €0.30 to €0.50 per inbox per month. At the recommended 50 accounts, the monthly cost is €0.60 to €1.00 per inbox.
For a 300-mailbox budget, Frostmailer Standard would cost €90 per month for three tenants. Maildoso’s 300-mailbox tier costs $225.00 per month before any domain charges on monthly plans. Add your sending-platform subscription to both.
Per-Inbox Guidance and Total Sending Volume
Price is only part of the comparison. You also need to check how many campaign emails each mailbox model is meant to send.
Sending guidance is not a technical cap. Frostmailer’s Microsoft tenants send about 200 emails per day in total. That works out to 2 to 3 campaign emails per inbox with 100 inboxes, or about 4 per inbox with the recommended 50 inboxes. The roughly 200 emails per day refers to a tenant, not each inbox.
Maildoso's per-mailbox sending guidance is not verified here, so check its documentation before planning volume.
Conclusion: Choose by Mailbox Requirements
Choose by mailbox access, not mailbox label. Match your requirements to what each provider offers:
| Requirement | Best fit and what to verify |
|---|---|
| Outlook access | Frostmailer provides Microsoft Azure/Outlook mailboxes. Maildoso uses SMTP and does not provide a Microsoft-hosted inbox. |
| Microsoft auth/OAuth | Choose Frostmailer if you need Microsoft sign-in. SPF, DKIM, and DMARC secure the domain, not Microsoft mailbox access. |
| SMTP credentials | Maildoso supplies SMTP mailboxes. Frostmailer does not sell standalone SMTP mailboxes. |
| Domain control | Check domain ownership, DNS access, and cancellation terms before buying. |
| Total cost | Compare the total cost per usable inbox for the mailbox type you need, not just the listed price or account count. |
| Bulk provisioning | Choose Frostmailer to expand Microsoft tenants or Maildoso for SMTP volume. Check provisioning and sequencer compatibility before placing a large order. |
Before paying, confirm ownership terms and get Frostmailer’s refund and handoff terms in writing. Its terms state that fees are generally non-refundable once inboxes have been delivered and setup is complete.
The right mailbox type does not guarantee placement. Results still depend on authentication, domain reputation, list quality, copy, sending behavior, reply activity, platform setup, and provider enforcement.
FAQs
How can I verify that my inboxes are Microsoft-hosted?
Check your provider’s documentation and account configuration for a dedicated Microsoft tenant, or review the mailbox connection settings in your sending platform. Frostmailer offers Microsoft Azure Tenant mailboxes with Microsoft 365 functionality.
Generic SMTP mailboxes typically aren’t native Microsoft-hosted inboxes. Maildoso states that it doesn’t support Microsoft 365 or Azure environments. Instead, it provides independent SMTP infrastructure.
How many inboxes do I need for my sending goals?
To estimate how many inboxes you need, divide your target daily sending volume by your provider’s daily per-inbox limit. That’s generally 15 emails for Google Workspace and about 4 for Microsoft Azure at 50 inboxes per tenant (about 200 per tenant a day).
Plan for the required warm-up periods, too. These strict sending caps help protect deliverability. To send more, add inboxes and domains rather than exceed per-inbox limits.
What access should I secure before a client handoff?
Before handing over mailboxes, secure full administrative access and record account credentials or ownership details. Check that SPF, DKIM, and DMARC are set up correctly for every associated domain.
Confirm that all mailboxes have completed the required warm-up period before using them for production sending. Mailboxes are typically linked to active subscriptions, so access may be revoked if the subscription is canceled.