Ensure Direct Send submissions are rejected

MediumLevel 2Manual reviewm365

Description

Direct Send is a method used to send emails directly to an Exchange Online customer’s hosted mailboxes from on-premises devices, applications, or third-party cloud services using the customer’s own accepted domain. This method does not require any form of authentication because, by its nature, it mimics incoming anonymous emails from the internet, apart from the sender domain. The recommended state is to configure RejectDirectSend to True. Direct Send allows devices and applications to transmit unauthenticated email directly to Exchange Online. While this method may support legacy systems such as printers or scanners, it introduces significant security risks: - Unauthenticated Email Delivery: Direct Send does not require authentication, making it an attractive vector for threat actors to deliver spoofed or malicious emails that appear to originate from trusted internal sources. - Phis...

How it is checked

Audit method: Manual review

This recommendation cannot be checked automatically. A scan lists it with these instructions when you pass --include-manual.

To audit using PowerShell: 1. Connect to Exchange Online using Connect-ExchangeOnline. 2. Run the following PowerShell command: Get-OrganizationConfig | fl RejectDirectSend 3. Verify that the value returned for RejectDirectSend is True.

How it is fixed

Fix method: Guidance or infrastructure patch

To remediate using PowerShell: 1. Connect to Exchange Online using Connect-ExchangeOnline. 2. Run the following PowerShell command: Set-OrganizationConfig -RejectDirectSend $true

Properties

Operating systems: Any
Tags: m365saas
Reference: CIS Microsoft 365 Foundations Benchmark v7.0.0 - 6.5.5 Ensure Direct Send submissions are rejected