Inframail alternatives: Microsoft-based sending, assessed

Providers in Inframail's category sell Microsoft 365-based outreach mailboxes, usually at a flat rate with a generous or unlimited mailbox count. If you are comparing alternatives, the number that decides your capacity is not the mailbox count. It is the per-mailbox sending rate you can sustain without throttling, multiplied by how many mailboxes you can realistically keep warm. Those two numbers are what to ask about.

"Unlimited inboxes" is a pricing feature, not a capacity feature

Every mailbox you add is another sending identity that needs warming, monitoring and its own reputation. Fifty cold mailboxes do not give you fifty mailboxes of capacity; they give you fifty things that can get filtered, and a month of warm-up before any of them is useful.

Capacity on a Microsoft-based setup is bounded by:

• Per-mailbox recipient and rate limits enforced by Exchange Online. These exist regardless of what the reseller's pricing page says, and they are not negotiable by your vendor.
• Tenant-level throttling. A tenant that suddenly emits a lot of outbound mail gets slowed or restricted. If your mailboxes share a tenant with other customers, their behaviour shapes yours.
• Warm-up time. A new mailbox that jumps to its theoretical ceiling in week one gets filtered, and the ceiling becomes irrelevant.
• Outbound spam policy. Microsoft has its own outbound thresholds; cross them and the mailbox or tenant gets restricted from sending, which is a different and more abrupt failure than "mail goes to spam".

The questions worth asking an alternative

Treat current pricing and feature claims in this category as unverified until the vendor confirms them to you in writing. Providers here launch, pivot and close quickly.

Microsoft sending behaves differently from Google sending

This catches people who move between the two.

• Outlook.com, Hotmail and Live are consumer Microsoft and filter differently from corporate Microsoft 365 tenants, which add their own layered policies, connection filtering and per-organisation rules. Your prospect at a 500-person company is behind a configuration you cannot see.
• Gmail publishes requirements you can check against: authentication with SPF and DKIM, DMARC on the sending domain, one-click unsubscribe for bulk senders, and a reported spam rate under 0.3%. Microsoft does not publish an equivalent spam-rate number, which means you cannot self-diagnose from a dashboard the way you can with Gmail. You have to measure placement.
• Reputation is per sending domain and per mailbox on both, but Microsoft tenants also carry organisation-level signals. Two mailboxes in the same tenant are not independent.

The practical consequence: if your prospect list skews Microsoft, test on Microsoft. An average placement figure across providers hides exactly the failure you are trying to find.

How to evaluate a replacement in two weeks

1. Provision three mailboxes with the candidate, on domains registered in your registrar account.
2. Verify authentication from the recipient side. Raw headers should show spf=pass, dkim=pass with your sending domain in the DKIM d= tag, and dmarc=pass.
3. Publish _dmarc yourself at p=none with a reporting address, confirm you can edit it, and read the first week of reports.
4. Confirm the connection method. If it is basic SMTP AUTH with a password, ask when OAuth is coming.
5. Warm each mailbox gradually with genuine two-way engagement for at least two weeks, with no live campaign attached.
6. Measure inbox placement separately for Gmail, Outlook.com and Microsoft 365 recipients, and compare against your existing mailboxes in the same week.
7. Only then move one segment across, and keep the old mailboxes warm.

What not to do

Do not add mailboxes instead of fixing a complaint rate. Spreading the same unwanted mail across more senders raises the number of restricted mailboxes, not the number of replies.

Do not run everything in one tenant. If every mailbox you own sits in a single tenant, one outbound-spam restriction stops all of your sending at once.

Do not use your company's production Microsoft 365 tenant for cold outreach. A sending restriction there stops invoices, support replies and calendar invites too.

Do not accept a vendor-held registrar account. You will discover the cost of that on the day you want to leave.

Do not assume a warm Gmail mailbox implies a warm Outlook one. Warm-up and reputation are per mailbox, and the two provider families judge you separately.

Where MailPilot fits

MailPilot warms Microsoft mailboxes over OAuth, which keeps working as basic authentication goes away, and warms Gmail over OAuth or any SMTP/IMAP sender including SendGrid, Amazon SES, Mailgun, Postmark and custom SMTP. It checks SPF, DKIM and DMARC per sending domain, measures real inbox placement per provider through a seed-inbox network, and tracks per-mailbox reputation daily — so you can compare two Microsoft-based providers on measured placement instead of on mailbox count.