ASD's Blueprint for Secure Cloud

Policy Filtering

This section describes the design decisions associated with Policy Filtering Microsoft 365 security features for system(s) built using ASD's Blueprint for Secure Cloud.

Estimated reading time: 2 minutes

Policy filtering within Office 365 Exchange Online Protection refers to the enforcement of Transport Rules.

Transport Rules are a set of rules enforced on mail transiting through the Exchange Organisation. Transport rules can be leveraged by Administrators to complete a number of actions on all mail or a subsection of the mail transiting through the Exchange Organisation. These items include:

  • Block mail with certain headers
  • Apply disclaimers to emails
  • Apply Office 365 message encryption

Transport Rules follow the following basic structure:

  • Conditions – Conditions identify which mail the transport rule applies to. These conditions largely target either information gained from message headers (e.g. the ’to’, ‘from’ or ‘CC’ fields) or message properties (e.g., size, attachments, subject, body, message classification). A single rule can have multiple conditions apply
  • Exceptions – Exceptions are an optional component of a Transport Rule and define the mail exempt from the rule
  • Actions – Actions are used to define what actions to undertake on the messages matching the conditions and which do not match any exemption. These actions include rejecting, deleting, redirecting the emails, and adding recipients, prefixes, and disclaimers. A single rule can have multiple actions applied however some actions are incompatible with others
  • Properties – Properties are used to define anything which do not fall into another category. This includes enforcing or testing the rule

Security & Governance

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Acknowledgement of Country
We acknowledge the Traditional Owners and Custodians of Country throughout Australia and their continuing connections to land, sea and communities. We pay our respects to them, their cultures and their Elders; past, present and emerging. We also recognise Australia's First Peoples' enduring contribution to Australia's national security.

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