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Jason
Asked: 2021-01-28 09:49:31 +0800 CST

Mail flow rule for email without an internal recipient

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I want to set up a mail flow rule which detects any email from outside the organization where To: and CC: don't specify an internal recipient (this would include emails which are bcc'd to internal users where the non-bcc'd recipients are exclusively outside the organization). Am I missing something?

This is meant as a mechanism for spam control.

I'm not really seeing any way to specify this in the mail flow rules though it could be done pretty easily with normal mailbox rules. Is there a way to do this at the organization level?

This is on Exchange Server from Office 365.

exchange email-server microsoft-office-365

1 Answers

  1. For transport rule, if we want to filter emails which are Bcc to an internal mailbox(Even if To field has an external email address), we could create a rule like the following:

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    After sending emails To/Cc/Bcc from an external email address to an office 365 mailbox, the emails will apply the transport rule when they are sent To/Cc:

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    If you want to block these Bcc emails, you could add the condition(The To or Cc box contains a member of (Distribution or Dynamic Distribution Group which includes your internal mailboxes)) to an exception, and Do the following ... (Reject/Delete emails), the following rule is for your reference:

    enter image description here

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