Posts

In this post, you will learn what Direct Send is, how attackers can abuse it, and how to block its use. Direct Send is a method used to send emails directly to Exchange Online hosted mailboxes from on-premises devices, applications, or third-party cloud services, using the MX record endpoint of your accepted domain in Exchange Online. This method assumes that SPF, DKIM, and DMARC are properly configured for your accepted domain. Any sender using Direct Send without being included in the SPF record of the accepted domain will already struggle to deliver messages successfully to your internal inboxes. ...

In this post, I will explain what PGP is, how it differs from S/MIME, and why encrypting and signing your emails is more important than ever. What is PGP? Pretty Good Privacy (PGP) is an encryption program that offers authentication and cryptographic privacy. Unless you take precautions, email is still one of the least secure ways to communicate. To keep your correspondence private and impenetrable, PGP provides a strong method for encrypting and signing your emails. ...

In this post, I’ll explain what RFC compliant emails are, share examples, and discuss what this means for senders. Especially those who may unknowingly be using improperly formatted sender addresses. Microsoft 365’s enhanced detection Recently, Microsoft has made a significant improvement in how it detects and handles non-RFC compliant emails. Microsoft has enhanced its detection mechanisms to better identify these types of messages, helping to protect users from potential risks. ...

In this blog post, we’ll walk through practical strategies to reduce the likelihood and impact of successful AiTM phishing attacks in Microsoft 365. In today’s threat landscape, adversary-in-the-middle (AiTM) phishing attacks have emerged as a particularly dangerous tactic. These attacks bypass traditional defenses by placing a malicious proxy between the user and the legitimate service, capturing credentials and session tokens in real time. Once attackers have session tokens, they can bypass even multi-factor authentication (MFA), making AiTM attacks especially difficult to defend against. ...

False positives block important emails, while false negatives allow harmful ones through. Learn how to manage these emails effectively in Microsoft Defender for Office 365. How inbound email works in Microsoft 365 To understand why your environment experiences false positives and false negatives, you first need to understand how Microsoft 365 handles inbound email. Microsoft 365 uses implicit email authentication to determine the final verdict for inbound messages. This approach goes beyond traditional SPF, DKIM, and DMARC checks by incorporating additional signals to evaluate inbound email. By leveraging these extra signals, emails that would typically fail standard authentication can pass implicit authentication and be successfully delivered to Microsoft 365. ...

A security.txt file is an industry standard used by organizations to provide a clear point of contact for vulnerability reporting. This blog will walk you through implementing a signed security.txt file using PGP (Pretty Good Privacy). Introduction The security.txt file, typically hosted at /.well-known/security.txt, provides a standardized way for security researchers to find the correct point of contact for reporting vulnerabilities. It helps ensure that security issues are directed to the right people quickly and efficiently. While it’s recommended to optionally sign the file with a PGP key for added authenticity, the primary goal is to clearly list how to reach your security team or responsible contact. Below, we’ll cover how to create a straightforward, effective security.txt file for your site. ...

In this post, you will learn what BIMI is, how it works, and the benefits it brings to your domain, including increased trust and brand visibility. In today’s digital age, making a memorable first impression is crucial. With the increasing volume of emails, standing out in the inbox can be challenging. That’s where BIMI (Brand Indicators for Message Identification) comes in, transforming how brands interact with recipients through email. ...

This blog post explains how an MTA-STS policy works and how to implement it on GitHub Pages. MTA-STS (Mail Transfer Agent Strict Transport Security) is a security protocol that enforces the use of secure TLS connections for inbound email communication. It helps protect your domain from TLS downgrade and man-in-the-middle attacks by ensuring that incoming emails are encrypted with TLS when delivered to your mail servers. When an external mail server (SMTP client) attempts to send email to your domain, it checks your MTA-STS policy to determine whether TLS encryption must be enforced. ...

In this post, you will learn how to enable and use SMTP DANE with DNSSEC in Exchange Online. While outbound SMTP DANE with DNSSEC in Exchange Online has been enabled since 2022, Microsoft is has rolling out inbound SMTP DANE with DNSSEC in Exchange Online since late 2024. For a deeper understanding of DNSSEC and DANE, take a look at my earlier blog post. How SMTP DANE with DNSSEC works SMTP DANE is a security protocol that uses DNSSEC to verify the authenticity of TLS certificates used for securing email communication. It helps protect against attacks such as TLS downgrade and man-in-the-middle attacks by ensuring that the certificates and encryption settings used in mail server communications are authentic and trustworthy. ...

Safe Attachments scans and evaluates attachments for malicious content before delivering messages to recipients. What you can manage with a Safe Attachments policy With a Safe Attachments policy, administrators can configure an additional layer of protection against malicious content in email attachments. Safe Attachments scans and evaluates attachments in a virtual environment before delivering messages to recipients. You can create a custom policy to, specify actions for unknown malware, select a quarantine policy, and configure global settings to protect files in SharePoint, OneDrive, and Teams with Safe Attachments. ...