Posts

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 verify inbound email. 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. Adding a signed security.txt file to your webserver enhances credibility and ensures trust, as the signature allows others to verify its authenticity. This blog will walk you through implementing a signed security.txt file using PGP (Pretty Good Privacy). Introduction The security.txt file is typically hosted at /.well-known/security.txt on a webserver. It follows a standardized format to share security contact information, preferred encryption keys, and disclosure policies. However, without proper authentication, anyone could tamper with the file. A signed security.txt solves this issue by letting others verify the file’s legitimacy using your PGP key. Here’s how to create, sign, and verify a security.txt file for your webserver. ...

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. It scans and evaluates attachments (Safe Attachments opens files 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. ...

This blog post explains the role and benefits of ARC sealing. ARC (Authenticated Received Chain) is an email authentication protocol that preserves the authentication results of an email as it travels through multiple intermediaries, such as forwarding services. Using ARC helps organizations handle the complexities of email authentication, especially when emails are forwarded. ARC involves multiple servers working together based on mutual trust. ARC ensures that legitimate emails are less likely to be marked as spam or rejected, while fraudulent emails are more easily identified and filtered out. In this blog post, we will explore the basics of ARC, how it works, and the benefits it provides. ...

Improve email security in Microsoft 365: Fine-tuning DKIM, configuring DMARC for the MOERA domain, and blocking inbound DMARC failures from reaching user inboxes. Fine-tune DKIM by frequently rotating the DKIM keys After setting up DKIM in Microsoft Defender for Office 365, it is also important to set up frequent rotation of these DKIM keys to prevent adversaries from intercepting and decrypting your cryptographic keys. Key rotation helps to minimize the risk of compromising the private keys. In Microsoft 365, you can rotate the DKIM keys for your domains to increase security. The recurrence must be every 3 months because rotating the DKIM keys every 3 months ensures a complete rotation of both selectors every 6 months. You can rotate the DKIM keys manually using the Defender portal or Exchange Online PowerShell, but it is easy to forget if you do it manually. So you should delegate this to Azure Automation by using the runbook below: ...