Outlook has a junk filter of its own, and that trips people up: there are two barriers running, in different places, and only one of them protects you on every device. Understanding the difference is half the job.
| Where it runs |
What that means for you |
| On the server, before it arrives |
Analyses the message before delivering it. It covers Outlook, your phone and webmail — all at once |
| In Outlook, on your computer |
Only acts after the message is downloaded, and only on that computer. On your phone, the same spam keeps arriving |
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Start from the right end: switching on the server filter pays off far more than any Outlook rule, because it cleans the mailbox everywhere at once. It is set out step by step in how to stop spam reaching your mailbox. After that, use Outlook for what is left.
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In classic Outlook (2016, 2019, 2021 and Microsoft 365)
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On the Home tab, click Junk and then Junk E-mail Options.
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| 2 |
On the Options tab, choose the Low level. It is the right balance for a work mailbox: it catches the obvious without starting to hide messages from customers.
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Under Blocked Senders, add the addresses that keep coming. If the nuisance always comes from the same domain, block the whole domain instead of chasing addresses one by one.
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Under Safe Senders, add your customers, your accountant, your bank — and tick the option to also trust e-mail from your Contacts. That is what stops you losing important messages.
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Do not choose "Safe Lists Only": that level sends to junk everything from anyone not already on your list. In a business mailbox that means losing the first e-mail from every new customer — precisely the messages that matter most. And never enable the option to permanently delete junk: what it deletes goes to no folder at all.
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In new Outlook and Outlook on the web
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Open Settings (the gear icon) and go to Mail → Junk email.
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Under Blocked senders and domains, add what you want stopped. Under Safe senders and domains, whatever must never go to junk.
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For anything that repeats in different shapes, create a rule under Mail → Rules — by subject, by word, by domain.
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The detail that catches people out with IMAP
Your account with us is IMAP, which means the folders live on the server and look the same everywhere. But Outlook's rules and junk filter are not folders: they are stored on that computer. Two practical consequences:
| What you will notice |
Why |
| Your phone keeps getting the spam |
The rule you made in the office Outlook does not exist on the phone — only the server filter acts on both |
| Marking as junk in Outlook does not teach the server |
It trains the local filter. To train the server one, move the message to the Spam folder from webmail |
| Reinstalling Windows wipes it all |
Blocked senders and rules go with the installation. The server lists stay |
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Worth checking: in your Outlook account settings, confirm that the junk folder points at the server's Spam folder rather than a local one. That way what goes to junk is the same on every device.
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If one of our messages lands in junk
It happens with invoice notices and support replies. Add your brand's domain to Safe Senders and it goes away. If it is the other way round — your messages landing in other people's spam — that is a different subject, covered in how to write an e-mail that does not land in spam.
If Outlook is throwing errors rather than over-filtering, see the most common Outlook errors or talk to us.
