News
GitHub Code Leak, 7-Eleven Breached, NYC Patient Exposure – Cybersecurity News [May 18, 2026]
Massive cyberattacks hit GitHub, 7-Eleven, NYC hospitals, and more. Explore the biggest cybersecurity threats and breaches from May 18, 2026.
Blog
Email security, in plain English.
Practical guidance on SPF, DKIM, DMARC, BIMI, phishing protection, and the parts of email infrastructure that quietly break things. Written by the DuoCircle team for people who run email and want to stop getting paged.
Browse by topic
Announcements (381) Email Security (303) Phishing Protection (150) DMARC (127) Email Services (77) Email Hosting (50) Data Privacy (38) Outbound SMTP (26)
Intermediate
Preventing Business Email Disruption Through An Invalid DKIM Selector Fix Process
Prevent business email disruption by fixing invalid DKIM selectors quickly to improve email authentication, deliverability, and domain trust.
Intermediate
20 Common Threats To Domain Reputation Protection And How To Avoid Them
Learn the top threats to domain reputation and how to avoid them to keep your email and online presence secure.
Intermediate
20 Common Threats To Domain Reputation Protection And How To Avoid Them
Learn the top threats to domain reputation and how to avoid them to keep your email and online presence secure.
Foundational
What Is GPS Spoofing? A Detailed Guide
Learn what GPS spoofing is, how it manipulates location data, the risks it creates, and the methods used to detect and prevent spoofing attacks.
Intermediate
Using Machine Learning For Malicious Email Detection And Phishing Defense
Machine learning helps detect malicious emails and phishing attacks faster, improving email security and reducing cyber threats.
Intermediate
7 Quick Fixes For SPF Authentication Failure In Microsoft 365 And Exchange Online
Fix SPF authentication failures in Microsoft 365 and Exchange Online with 7 quick solutions to improve email delivery, stop spoofing, and protect domains.
News
Cisco SD-WAN Flaw, Critical NGINX Exploit, Foxconn Ransomware Attack – Cybersecurity News [May 11, 2026]
Critical cybersecurity threats emerge as Cisco SD-WAN, NGINX, Microsoft Exchange, and PAN-OS flaws face active exploitation worldwide.
Foundational
11 Common Malware Types and How to Spot Them
Learn about 11 common malware types, how they spread, and the warning signs to help protect your devices and data online.
Email Services 8 min
5 Reasons To Test SPF Configuration Before Sending Emails
Testing your SPF configuration before a campaign goes live is a core part of modern email authentication.
Email Security 13 min
Your Vendors Are Your Weakest Link: How Third-Party Email Compromise Doubled in One Year and What SMBs Can Do About It
A data-driven analysis with 20+ primary-source statistics from Verizon, IBM, SecurityScorecard, the FBI, the World Economic Forum, and others.
Email Services 8 min
How To Validate A DMARC Record Generator Output Before Publishing DNS Changes
A DMARC record generator can simplify the process of creating a DMARC policy, but generating the record is only the first step.
Announcements 8 min
Zara Data Exposed, Medtronic Cyberattack Confirmed, Trellix Repository Breached – Cybersecurity News [May 04, 2026]
Here’s your weekly roundup of the most important cybersecurity stories from the past week, covering major data breaches, critical vulnerabilities.
Email Services 8 min
7 DKIM DNS Configuration Strategies For Hybrid Cloud Email Systems
Contemporary businesses seldom depend on a singular email setup.
Email Security 5 min
Email Monitoring Tools: A Complete Guide to Protecting Your Email Ecosystem
Email continues to be one of the most essential communication channels for businesses—but it’s also one of the most targeted by cyber threats.
Cybersecurity 19 min
The State of Cybersecurity in 2026: What the Data Tells Us, What It Means, and What to Do Next
A data-driven analysis of 26 primary-source statistics from institutional reports by the World Economic Forum, IBM, Verizon, Cisco, Accenture, ISC2, NIST.
Email Services 8 min
SPF Lookup Failure Troubleshooting: Why Your SPF Record Breaks And How To Fix It
Email authentication serves as the foundation for effective email deliverability.
Email Security 8 min
BIMI in 2026: What the Certificate Authority Does, and What Your DMARC Tool Does
BIMI confuses buyers because two different vendors handle two different jobs. Here is the clean split between VMC procurement (a Certificate Authority function) and BIMI hosting (what your DMARC reporting tool actually does).
SPF Records 7 min
When SPF Lookup Limits Actually Break Things: The 10-Lookup Rule, Permerror, and How to Stay Under It
The SPF 10-DNS-lookup limit silently breaks email authentication once you exceed it. Here is how to diagnose a permerror, why even careful organizations end up over the limit, and the fix options that actually work.
Outbound SMTP 7 min
Office Copiers Can't Authenticate to Microsoft 365 Anymore: Why It Broke and How to Fix It
Your scan-to-email died after a Microsoft 365 update. Here's why basic auth and SMTP AUTH got disabled, the three options your IT team actually has, and the fastest reliable fix.
Email Services 7 min
11 SPF Validation Tool Checks You Should Run Before Sending Bulk Emails
Email marketing campaigns have the potential to enhance engagement, boost conversions.
DMARC 7 min
DMARC at p=none Is a Setup State, Not a Deployment
Publishing a DMARC record at p=none is the starting line, not the finish line. Here is what p=none actually does, what it does not, and how to move to enforcement without breaking legitimate mail.
Announcements 12 min
Medtronic Cyberattack Confirmed, cPanel Ransomware Wave, Root Access Granted , Cybersecurity News [April 27, 2026]
Here’s your weekly roundup of the most significant cybersecurity stories from the past week, covering major data breaches, critical vulnerabilities.
Email Services 6 min
How Poor Email Testing Is Silently Costing SaaS Companies Thousands
Email is one of the most critical communication channels for SaaS companies.
Email Security 12 min
Shadow AI in the Inbox: How Employees Using Unauthorized AI Tools Are Creating a New Email Security Crisis
A data-driven analysis with 20+ statistics from Verizon, IBM, Cisco, KPMG, LayerX, Microsoft, the World Economic Forum, and others.
SPF Records 8 min
How SPF Record all Affects Email Routing Across Hybrid Cloud Environments
In today’s digital landscape, especially within hybrid cloud frameworks, email authentication has become increasingly vital.
DMARC 5 min
Why DIY-ing DMARC could cost you more than you think
Why DIY-ing DMARC could cost you more than you think.
Email Services 7 min
7 Critical Factors to Consider Before You Buy SMTP Relay Services
Email remains an essential communication tool for businesses, utilized for everything from transactional notifications to marketing initiatives and customer.
Email Security 12 min
DMARC, SPF, and DKIM in 2026: Why Email Authentication Is Now a Regulatory Requirement, Not Just a Best Practice
A data-driven analysis with 20+ statistics from EasyDMARC, Google, Microsoft, IBM, Verizon, CISA, and the PCI Security Standards Council.
Email Security 8 min
Designing A Custom Dkim Architecture For High-Volume Email Senders
Organizations that send large volumes of emails, including software-as-a-service (SaaS) platforms, marketing automation providers.
Phishing Protection 11 min
AI-Generated Phishing Has Eliminated the Typo: Why Traditional Email Filters Are No Longer Enough
A data-driven analysis for security leaders, IT teams, and MSPs, with 20+ primary-source statistics from Microsoft, IBM, FBI IC3, KnowBe4, Verizon, Cisco.
Announcements 5 min
Sri Lanka Cyberattack, SilentGlass Threat Defense, Rituals Data Breach, Cybersecurity News [April 20, 2026]
Sri Lanka Cyberattack, SilentGlass Threat Defense, Rituals Data Breach, Cybersecurity News [April 20.
Email Services 8 min
How To Migrate From Windows SMTP Server To Cloud-Based SMTP Without Downtime
Transitioning from a Windows-based SMTP server to a cloud-hosted solution has evolved beyond simple modernization; it’s now a key strategic initiative aimed at.
Email Services 17 min
Trust by Design: Rethinking DKIM Settings for Modern Email
Email trust is no longer a background technical detail, it’s the foundation of how brands communicate, protect users.
Email Services 16 min
5 Best DKIM Record Examples To Understand Selectors, Key Lengths, And TXT Formatting
Why these DKIM record examples matter A well-formed DKIM record is the foundation of email authentication.
Announcements 5 min
UK Cyber Surge, Poland Incident Surge, Japan Shipping Attack, Cybersecurity News [April 13, 2026]
UK Cyber Surge, Poland Incident Surge, Japan Shipping Attack, Cybersecurity News [April 13.
Email Security 5 min
Enterprise email security: Here’s what you should know about it
When your organization operates at scale, emails don’t go out from one domain; they are sent from marketing platforms, HR systems, finance tools.
Email Security 18 min
Behind the Signature: A Curious Journey into DKIM Implementation
Every verified email has an unseen signature that plays a crucial role in establishing trust.
Email Security 9 min
9 Reliable Providers for a Managed outgoing SMTP email server Solution
In the fast-moving digital world of today, effective email delivery is essential for businesses that rely on smooth communication and customer interactions.
Email Security 9 min
The Signature Checkpoint: DKIM Testing at the Gates of the Inbox
As email security continues to advance, the inbox serves as a crucial entry point, with DKIM testing playing an essential role in its protection.
Announcements 5 min
Apple Pay Scam, Crypto Fraud Victims, Retirement Phishing Loss, Cybersecurity News [April 06, 2026]
Apple Pay Scam, Crypto Fraud Victims, Retirement Phishing Loss, Cybersecurity News [April 06.
DMARC 9 min
How ARC resolves email authentication for forwarded messages
How ARC resolves email authentication for forwarded messages.
Email Security 9 min
Avoiding Burn: How An SPF Generator For Godaddy Can Still Toast Your DMARC If Misused
The Sender Policy Framework is deceptively simple: publish a single SPF record as a TXT record in your domain DNS so receiving systems can check whether a.
Email Security 15 min
12 Best Hosted SMTP Servers for High Deliverability in 2026
Selecting the appropriate hosted SMTP server in 2026 is crucial for getting your emails delivered to the inbox rather than the spam folder.
Email Hosting 14 min
Inbox Wars: Winning with Powerful SMTP Email Hosting
In the bustling digital environment of today, the quest for consumer attention often starts with the inbox.
Announcements 5 min
LinkedIn Fraud Spike, SIM Scam Bust, UK VIPs Targeted, Cybersecurity News [March 30, 2026]
LinkedIn Fraud Spike, SIM Scam Bust, UK VIPs Targeted, Cybersecurity News [March 30.
Email Services 9 min
8 Genius Tricks to Master Your DKIM Validator Like a Pro
Navigating email authentication can often feel overwhelming, particularly when it comes to DKIM validation and ensuring your emails reach their intended.
Email Security 6 min
What happens when your DKIM key is compromised? How can you identify and fix the problem?
What happens when your DKIM key is compromised? How can you identify and fix the problem?
Phishing Protection 6 min
How Domain Verification Helps Prevent Email Phishing Attacks
Email is still the most exploited initial vector of attacks in cybersecurity.
Email Services 15 min
Set Up A DKIM Key For Microsoft 365 Custom Domains: A Step-By-Step Guide
This step-by-step guide explains how to prepare your Microsoft 365 tenant and custom domain to publish a DKIM record.
Email Security 15 min
How The Best Anti-Phishing Software Prevents Email-Based Attacks
Email-centric threats continue to be a prevalent and expensive cybersecurity challenge for both companies and individuals.
Announcements 5 min
AI Phishing Campaign, TikTok Phishing Targeted, Dutch Police Cyberattack, Cybersecurity News [March 23, 2026]
AI Phishing Campaign, TikTok Phishing Targeted, Dutch Police Cyberattack, Cybersecurity News [March 23.
DMARC 5 min
Why is DMARC important for the retail sector?
Why is DMARC important for the retail sector?
Announcements 5 min
Horabot Resurfaces Mexico, Aura Breach Compromise, Tax Season Threats, Cybersecurity News [March 16, 2026]
Horabot Resurfaces Mexico, Aura Breach Compromise, Tax Season Threats, Cybersecurity News [March 16.
Email Security 7 min
VMC vs CMC explained: Which logo certificate should you choose?
VMC vs CMC explained: Which logo certificate should you choose?
Announcements 4 min
Cambodia Targets Cybercriminals, Traditional Security Insufficient, AI Against Phishing, Cybersecurity News [March 09, 2026]
Cambodia Targets Cybercriminals, Traditional Security Insufficient, AI Against Phishing, Cybersecurity News [March 09.
Email Security 8 min
8 Best Tools To Test DKIM Records And Fix Signature Errors
Email authentication is vital for safeguarding your domain against spoofing and enhancing email deliverability.
Email Services 16 min
Troubleshoot Failed Signatures Using A DNS DKIM Lookup And Record Inspector
Email authentication plays a critical role in protecting your domain from spoofing and ensuring that your messages reach recipients’ inboxes.
Email Hosting 18 min
10 Steps To Set Up A Self-Hosted Mail Server Without Hitting Spam
Self-hosted email gives you control, privacy, and the flexibility to run open source software instead of relying entirely on a mail service provider.
Cybersecurity 5 min
NCSC announces the retirement of Mail Check and Web Check: Here’s what it really means
NCSC announces the retirement of Mail Check and Web Check: Here’s what it really means.
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