Prewarmed Azure inboxes: 25, 49 or 100 per tenant

What a tenant is, and why the cost per inbox collapses

A tenant is your own Microsoft account, the kind a whole company would have. Instead of buying mailboxes three at a time, you get one account holding 100 mailboxes. Microsoft charges for it differently, which is why the cost per inbox drops by about ten times rather than by a few percent.

You get the account ID, a spreadsheet of all 100 mailboxes and their passwords, and the email records already set up.

The volume shape that makes this work

The reason to buy a tenant is not that it is cheap. It is that you can send the same number of emails in a much safer way. Fifteen hundred a day spread over 100 mailboxes is 15 each, which looks like a hundred people doing their jobs. The same 1,500 from 10 mailboxes is 150 each, which looks like exactly what it is.

Gmail and Outlook judge each sending address on its own behaviour. Spreading your sending across more mailboxes is the most effective thing a high-volume sender can do, and tenant pricing is what makes it affordable.

The risk you are taking on, stated plainly

Every mailbox in a tenant shares one reputation, so a single unchecked list can damage all of them at once. That is why density is a choice: 25 mailboxes to a tenant costs four times as much per inbox and contains the damage to a quarter as many. Clean your list first either way.

If you buy in packs and a domain stops working, you lose three inboxes. With a tenant, something serious can affect all 100 at once. That is the trade you make for the lower price, and anyone selling you a tenant without mentioning it is not doing you a favour.

So run it carefully. Only send to verified lists, start about twenty mailboxes at a time rather than all hundred, and check your bounce rate every day for the first two weeks. Teams who do this keep tenants running for a long time. Teams who treat them as cheap inboxes do not.