Where you saw it: Recipients at Microsoft-hosted domains finding your mail in junk, or a seed test showing inbox at Gmail and junk at Outlook.
Why it happens
- Low IP or domain reputation with Microsoft, visible in SNDS if you have access to it.
- A tenant-level rule set by the recipient's own administrator, which no sender can see.
- A user-level block or a previous spam report from that individual.
- Bulk mail landing in the Other tab of Focused Inbox, which is not junk and looks identical in your metrics.
- Content signals such as unfamiliar link domains or an unusual attachment type.
- Complaint rate above Microsoft's tolerance, which tightens filtering across their estate.
The fix, in order
Separate junk from Focused Inbox Other
They are different outcomes with different causes. Ask the recipient to look at which folder and which tab, because the fix differs completely.
Check SNDS for your own reputation
If you own the sending IPs, SNDS shows complaint rates and filter verdicts. It is the only view Microsoft offers into their judgment of you.
Confirm authentication passes and aligns
Exchange Online Protection weighs authentication heavily, and a DMARC failure moves you toward junk before content is considered.
Ask a business recipient to allowlist you
For a tenant-level rule this is the only real fix. Their administrator can add your domain to the allowed senders list in minutes.
Reduce complaints through the list itself
Mail engaged recipients, make unsubscribe easy, and stop sending to people who have ignored you for six months.
How to know it worked
The short version
- A seed test to Microsoft-hosted addresses shows inbox placement.
- SNDS shows a green status for your IPs.
- Recipients at the affected domain report receiving mail normally.
Questions people ask
Why does one person get it and another does not at the same company?
User-level rules and individual spam reports sit on top of the tenant policy. Two people in one office genuinely can get different outcomes for the same message.
Is Focused Inbox the same as junk?
No. The Other tab is still the inbox and the message was delivered. It looks like poor performance in your open rates and it is a different problem from filtering.
Can list cleaning fix Outlook filtering?
It helps by lowering bounces and improving reputation. It does nothing about tenant rules, user blocks or content signals, which are frequently the real cause.