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Office 365 Advanced Threat Protection (ATP) deep dive

Around 5 years ago (April 2015) Microsoft announced Exchange Online Advanced Threat Protection (ATP), which was renamed to Office 365 Advanced Threat Protection around a year later.

By using Office 365 Advanced Threat Protection you can add additional protection to the email filtering service available in Office 365 called Exchange Online Protection (EOP).

In this article, I will explain the functionality of Office 365 Advanced Threat Protection, and I will share the lessons learned while implementing the solution at several of my customers. I’ll also try to include as much references to other articles or blogposts as possible hopefully providing you with enough information for you to start implementing Office 365 ATP as well.

This article covers the following topics:

Disclaimer: This post reflects the status of Office 365 Advanced Threat Protection as of April 28 2020. Functionality may change, even right after this post has been published.

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Microsoft is going to disable basic/legacy authentication for Exchange Online. What does that actually mean and does that impact me?

Update: On April 3rd 2020, the Exchange Team announced that due to the COVID019 crisis, they will postpone disabling legacy authentication until the second half of 2021.

Update: On April 30 2020, the Exchange Team announced that OAuth 2.0 authentication for IMAP and SMTP AUTH protocols is now available. In order to leverage this functionality mail clients need to start using it (so they need an update). Michel de Rooij did a nice article on how to configure Thunderbird for oAuth2 which you can read here: Configuring Exchange Online with IMAP & OAuth2

Update: On May 28 2020, the Exchange Team announced that OAuth support for POP is now also available for Exchange Online.

Update: On June 30th 2020, the Microsoft Exchange Team announced support for Modern Authentication in scripts using the new Exchange PowerShell module, see: Modern Auth and Unattended Scripts in Exchange Online PowerShell V2

On March 7, 2018 the Microsoft Exchange Team announced that on October 13, 2020 it would stop the support for Basic Authentication (also called Legacy authentication) for Exchange Web Services (EWS) in Exchange Online (EXO), the version of Exchange offered as a service part of Office 365. EWS is a web service which can be used by client applications to access the EXO environment. The team also announced that EWS would not receive any feature updates anymore, and suggests customers to transition towards using Microsoft Graph to access EXO.

One and a half year later, on November 20, 2019 the Exchange Team also announced to stop supporting Basic Authentication for Exchange ActiveSync (EAS), Post Office Protocol (POP), Internet Message Access Protocol (IMAP) and Remote PowerShell on October 13 2020 as well. Authenticated Simple Mail Transfer Protocol (SMTP) will stay supported when used with Basic Authentication.

Instead of supporting Basic/Legacy authentication Microsoft will move towards only supporting Modern Authentication for most of the methods used to connect to Exchange Online.

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Stopping automatic email forwarding in your Exchange Online environment in a controlled way

Working as a modern workplace consultant also means that sometimes you have to go deep into Exchange Online options in order to make sure that (sensitive) data of your customer doesn’t leave the organization without the proper security measurements taken. In the Microsoft documentation titled: “Best practices for configuring EOP and Office 365 ATP“, the recommended settings for both Standard and Strict states that Auto-forwarding to external domains should be disallowed or monitored at least.

Automatic email forwarding is one of the possible and still most common way (sensitive) company data might leave the organization. Giving the users the ability to automatically forward emails using either mailbox forwarding or message rules to users outside the organization in that case can be very risky. I’ve seen many cases where corporate email accounts were configured to automatically forward all email to personal gmail.com or hotmail.com accounts. Also still enabled mailboxes which forward mail to users personal accounts while the user doesn’t work at the company anymore is common practice. 

It’s also commonly known that if a user somehow gets compromised, hackers usually put a forward on the mailbox of the user in order to gain knowledge about the user in order further continue with their attack methods, or to retrieve sensitive company data for their own gains.

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