A free Outlook.com mailbox shows ads, and a Microsoft 365 subscription is what removes them, but the ad free benefit only kicks in when a few specific conditions line up, which is why people sometimes pay for Microsoft 365 and still see ads afterward.
What actually qualifies for the ad free benefit
The ad free experience applies specifically to Outlook.com style addresses, meaning ones ending in @outlook.com, @hotmail.com, @live.com, or @msn.com, and only when that address is properly linked to an active Microsoft 365 subscription. If your Microsoft 365 subscription is tied to a Gmail address or another non Microsoft email as its account identifier, the ad free benefit does not extend to that inbox on its own.
If you subscribed with a non Outlook address
Add an Outlook.com alias to the Microsoft account that holds your subscription, then sign in to Outlook using that alias. Once the alias is properly associated with the active subscription, ads should stop appearing in that mailbox.
If you already have the right address and still see ads
Confirm the Outlook.com address is actually added inside whichever Outlook app or webmail client you are using, and not just present as an alias on the account in general. It is also worth confirming the subscription itself is genuinely active and not lapsed, since an expired subscription reverts the mailbox back to the free, ad supported experience even if the address and setup are otherwise correct.
If your organization is weighing personal Outlook.com accounts against a proper Microsoft 365 business setup, a business tenant gets you a lot more than an ad free inbox, including real identity management, security controls, and shared collaboration tools. Our Microsoft 365 and Modern Work team can help you figure out what actually makes sense. Get in touch if you want to talk it through.