Protection against phishing, malware, and other threats targeting email and collaboration tools in Microsoft 365
To block persistent spam in Office 365/Outlook, use both per-sender blocking and junk email settings.
- Block individual senders from messages
- In Outlook, right-click a spam message.
- Select Junk (or Block) > Block Sender.
- Future messages from that address will go directly to the Junk Email folder or to End-User Quarantine if configured.
- Add addresses or domains to Blocked senders (Outlook on the web / new Outlook)
- At the top of the page, select Settings.
- Select Mail > Junk email.
- Under Blocked senders and domains, choose Add blocked sender.
- Enter:
- A full email address to block a specific sender, or
- A domain (for example,
contoso.com) to block all senders from that domain.
- Select OK, then Save. Messages from those senders/domains will be delivered directly to Junk Email.
- Use Block or allow settings (Outlook Web App / Exchange Online mailbox)
- At the top of the screen, select Settings > Mail.
- Under Options, select Block or allow.
- In Blocked senders, enter the spam email addresses or domains in Enter a sender or domain here, then press Enter or select Add.
- Select Save.
- Optionally, to tighten filtering, enable Automatically filter junk email and use Safe Senders and Recipients so legitimate senders are not treated as junk.
- Periodically review Junk/Quarantine
- Check the Junk Email folder regularly to ensure legitimate messages are not being blocked.
- If End-User Quarantine is enabled by the administrator, review quarantined messages there as well.
If spam continues from many different addresses, an administrator should configure higher-level anti-spam policies in Microsoft Defender for Office 365, but that configuration is outside the provided context.
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