DMARC (Domain-based Message Authentication, Reporting, and Conformance) is a crucial email security protocol that prevents email spoofing, phishing attacks, and business email compromise by ensuring that only authorized sources can send email on behalf of a domain. By leveraging SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail), DMARC builds on these foundational email authentication methods to provide domain owners with granular control and visibility over their email traffic.
The Difference Between ~all, -all, and +all in SPF
by DuoCircle
SPF is the foundation of your email authentication, as it tells the receiving servers, “these are the only servers and addresses allowed to send emails on our behalf.” So, when an email goes out from your side to a provider like Gmail or Microsoft Outlook, their servers pull out your SPF record to confirm if the email came from a server you actually approved. If the server matches one of the entries in the list, the email is delivered.
Cyber incidents this week included ToddyCat deploying new tools to steal email data, Harvard reporting a breach affecting its alumni community, and a vendor compromise at SitusAMC exposing corporate records tied to major banks. Alongside, Asahi confirmed data theft affecting two million individuals, and OpenAI disclosed limited user information exposure linked to a Mixpanel breach. Here are this week’s top headlines.
You might have been sending emails using Gmail for years now, but that’s not a good enough reason for the Email Service Provider (ESP) to let your email in, even if it feels like something’s off. Since email-based attacks are becoming so frequent and rampant, your sender reputation and good faith no longer suffice, given today’s threat landscape. That is why Gmail and other ESPs verify every email they receive before delivering it to the recipient’s inbox.
How cybercriminals use DNS hijacking to bypass DMARC policies
by DuoCircle
Email authentication protocols like SPF, DKIM, and DMARC are supposed to stop attackers from pretending to be you and dupe your clients. But what if they target the very system that these protocols depend on?
Logitech Data Breach, Mass Router Hijack, Android Trojan Sturnus – Cybersecurity News [November 17, 2025]
by DuoCircle
Here are this week’s cybersecurity updates, bringing you headlines that made news around the world. Princeton University reported a data breach impacting alumni and donors, and the Clop extortion gang’s activity continued, with Logitech confirming data theft linked to a third-party zero-day.
DuoCircle, LLC (“Company”) hereby provides formal notice that all data associated with the discontinued MailHostingService.com email hosting platform has been permanently and irreversibly destroyed in accordance with applicable data protection regulations and industry best practices.
Gmail enforcement norms for non-compliant emails: What’s new in 2025?
by DuoCircle
Email-based cyberattacks have become so severe and rampant that you can no longer afford to make email security an afterthought. Attackers out there are ready to seize even the most seemingly insignificant vulnerabilities at every chance they get. If your outgoing emails are not protected with email authentication protocols like SPF, DKIM, and DMARC, you are essentially making it easier for attackers to steal your confidential data, deceive your customers, and install malware on their systems.
How email authentication helps you prove sender identity under ISO 27001
by DuoCircle
Email is one of the main ways companies talk to customers, partners, and even their own teams. Because it is used so much, it also becomes an easy target for attackers who try to pretend to be someone else or steal important information. When a business wants to follow ISO 27001, it needs to show that its messages are safe and really coming from the right sender. That is where email authentication becomes helpful.
Cybersecurity headlines this week show a clear picture, and no one seems immune. Hyundai confirmed a data breach that may have exposed millions of Social Security numbers, and Google has gone on the offensive, suing a China-based group accused of running a billion-dollar phishing operation.
![ToddyCat APT Evolving, Harvard Breach Reported, SitusAMC Vendor Breach– Cybersecurity News [November 24, 2025]](https://www.duocircle.com/wp-content/uploads/2025/12/spf-validator-5634.jpg)
![Logitech Data Breach, Mass Router Hijack, Android Trojan Sturnus – Cybersecurity News [November 17, 2025]](https://www.duocircle.com/wp-content/uploads/2025/11/hosted-email-server-4002.jpg)
![Hyundai Leak Exposed, International Malware Bust, Lighthouse Phishing Lawsuit – Cybersecurity News [November 10, 2025]](https://www.duocircle.com/wp-content/uploads/2025/11/spf-record-check-3501.jpg)