Spam filtering before redirecting email

KarolisSSSSS 21 Reputation points
2020-10-22T15:17:49.42+00:00

Hi, we O365 Exchange Online, we've created a shared mailbox and all incoming emails are redirected (automatically forwarded) to external email. If we receive spam email, it is redirected (forwarded) to external email and then goes to spam filter. Is it possible to set rules that first action would be going to spam filter and only if it is not a spam it is being redirected to external email address?

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Microsoft Exchange Online Management
Microsoft Exchange Online Management
Microsoft Exchange Online: A Microsoft email and calendaring hosted service.Management: The act or process of organizing, handling, directing or controlling something.
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Exchange Server Management
Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
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Accepted answer
  1. Lydia Zhou - MSFT 2,371 Reputation points Microsoft Employee
    2020-10-23T06:57:46.443+00:00

    @KarolisSSSSS

    What about creating an Inbox rule for shared mailbox to redirect or forward messages? If so, you have to create a transport rule to prepend the subject of those inbound messages, then you can create an Inbox rule like this: "messages with specific words in the subject (add by mail flow rule), redirect/forward to another user".

    For your reference: Add rules to a shared mailbox.


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  1. Andy David - MVP 138.6K Reputation points MVP
    2020-10-22T15:28:39.257+00:00

    Not possible since rules fires before the anti-spam checks.

    However... Anti-malware checks happen before a transport rule. Are you saying that malware messages are being forwarded as well?
    If so, I would use a transport rule to forward instead of forwarding from the mailbox and see if at least those are blocked

    If you want to mark specific messages as spam before they're even scanned by spam filtering, or mark messages so they'll skip spam filtering, you can create mail flow rules (also known as transport rules) to identify the messages and set the spam confidence level (SCL). For more information about the SCL, see Spam confidence level (SCL) in EOP.

    https://learn.microsoft.com/en-us/microsoft-365/security/office-365-security/use-mail-flow-rules-to-set-the-spam-confidence-level-scl-in-messages?view=o365-worldwide

    https://learn.microsoft.com/en-us/microsoft-365/security/office-365-security/exchange-online-protection-overview?view=o365-worldwide#how-eop-works

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