Foundational
Email Sender Verification: What The Blue Check Mark Really Means
Email sender verification explains what the blue check mark means, how it confirms sender identity, and why verified emails can improve trust and security.
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.
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Announcements (381) Email Security (303) Phishing Protection (151) DMARC (127) Email Services (77) Email Hosting (50) Data Privacy (38) Intermediate (31)
Foundational
Authoritative vs. Recursive DNS: Understanding the Key Differences
Learn the key differences between recursive and authoritative DNS, how they work together, and why DNS resolution, caching, and email security matter.
Intermediate
Campaign Monitor SPF: How To Configure And Verify Email Authentication
Configure and verify your Campaign Monitor SPF record to authenticate email, improve deliverability, prevent spoofing, and protect your domain reputation.
News
Microsoft Patch Tuesday, CISA Adds Flaws, Revolut Data Breach – Cybersecurity News [September 07, 2026]
Stay updated on the latest cybersecurity threats, including Microsoft flaws, ransomware, phishing, data breaches, and actively exploited vulnerabilities.
Tutorials
Hotmail DNS Records: SPF, DKIM & DMARC Setup Guide
Learn how to configure Hotmail DNS records with SPF, DKIM, and DMARC to improve email authentication, prevent spoofing, and boost message deliverability.
Tutorials
How To Add DKIM Public Key In DNS Cpanel: Step-By-Step Setup Guide
Learn how to add a DKIM public key in DNS cPanel with this step-by-step guide. Configure, verify, and troubleshoot DKIM records for secure email authentication.
Intermediate
The Security Gaps That Appear When Sales Teams Expand Across Borders
Discover the security gaps that emerge as sales teams expand globally, from data exposure and access risks to phishing threats and compliance challenges.
Foundational
Why Are My Emails Bouncing? Common Causes and How to Fix Them
Learn why emails bounce, from full mailboxes and invalid addresses to SPF, DKIM, DMARC, blocklisting, and sender reputation issues, with practical fixes.
Tutorials
Constant Contact SPF Record: How To Set Up And Verify It
Learn how to set up and verify a Constant Contact SPF record to improve email authentication, strengthen email security, and support better deliverability.
Tutorials
NetSuite SPF Record: How Configure, Validate And Troubleshoot
Learn how to configure, validate, and troubleshoot a NetSuite SPF record to improve email authentication, prevent spoofing, and strengthen email deliverability.
News
Berlin Ransomware Theft, Eastlink Data Breach, Dark Web Exposure – Cybersecurity News [August 31, 2026]
Cybersecurity news highlights Berlin ransomware, the Eastlink data breach, dark web ID exposure, zero-day exploits, malware, and espionage threats.
Tutorials
How to Set Up SPF and DKIM for Campaign Monitor
Learn how to set up SPF and DKIM for Campaign Monitor, troubleshoot authentication issues, and improve DMARC alignment and email deliverability for your domain.
Foundational
URL Blacklist Explained: How Email Security Systems Block Malicious Links
Learn how URL blacklists help email security systems detect, block, and prevent malicious links, phishing attacks, and dangerous websites from reaching users.
Tutorials
Network Solutions SPF Record: How To Add And Configure SPF
Configure a Network Solutions SPF record to authorize trusted email senders, prevent spoofing, improve email security, and support better email deliverability.
Advanced
12 DNS Scanning Techniques for Domain Intelligence and Email Security
Discover 12 DNS scanning techniques to improve domain intelligence, identify risks, strengthen email security, and protect your organization from threats.
Foundational
Why I Moved My Company Email Off Google After Seven Years
Discover why one company moved from Google Workspace to self-hosted email, cutting costs, gaining data control, and maintaining 99.7% email deliverability.
News
ShinyHunters Target McKesson, Boston Scientific Cyberattack, Hasbro Breach Disclosed – Cybersecurity News [August 24, 2026]
Cybersecurity roundup: McKesson, Boston Scientific and Hasbro breaches, airport attacks, ransomware, critical flaws, AI threats and urgent security updates.
Intermediate
How To Build A Cybersecurity Team That Protects Email In The Cloud
Build a cybersecurity team that protects cloud email, prevents cyber threats, secures data, and strengthens your organization’s overall security posture.
Foundational
6 Effective Data Loss Prevention Strategies for Business Email Security
Discover 6 effective DLP strategies to secure business email, prevent data loss, protect sensitive data, and strengthen email security against online threats!
Comparisons
DNS A Vs AAAA Records: Key Differences And When To Use Each
Learn the key differences between DNS A and AAAA records, how they work, and when to use each for reliable IPv4 and IPv6 connectivity across networks.
Intermediate
Why I Moved My Company Email Off Google After Seven Years
Discover why I moved my company email off Google after seven years, from privacy concerns and data control to security, costs, and a better email experience.
Intermediate
7 DKIM Configuration Checks for IONOS Before Sending Emails
Discover 7 essential DKIM checks for IONOS to verify DNS records, selectors, alignment, and email authentication before sending business emails.
Tutorials
DKIM Network Solutions: DNS, TXT Setup And Troubleshooting
Set up DKIM on Network Solutions with ease. Learn DNS and TXT record configuration, common errors, and troubleshooting tips for better email security.
News
Entra ID Vulnerability, Zombie Card Attack, AI Exploit Threats – Cybersecurity News [August 17, 2026]
Stay updated on the latest cybersecurity threats, including critical vulnerabilities, AI-driven attacks, ransomware, data breaches, malware, and zero-days.
Guides
10 SPF Record Zendesk Checks Before Sending Customer Emails
Learn 10 essential SPF record checks for Zendesk to verify email authentication, prevent delivery issues, and improve customer email trust and security.
Tutorials
Reverse DNS Does Not Match SMTP Banner: Causes, Fixes, and Best Practices
Fix reverse DNS and SMTP banner mismatches with practical steps to align PTR, A, MX, HELO, and SMTP settings and improve email deliverability.
Foundational
How SOA Records Support Reliable DNS Zone Transfers
Discover how SOA records support reliable DNS zone transfers by coordinating DNS updates, synchronization, refresh intervals, retries, and server communication.
Tutorials
10 Steps to Validate Your Qualtrics SPF Record Before Launch
Learn 10 essential steps to validate your Qualtrics SPF record before launch, prevent authentication errors, improve email security, and boost deliverability.
News
DentaQuest Data Breach, CEVA Customer Exposure, Levi Strauss Attack – Cybersecurity News [August 10, 2026]
Explore this week’s top cybersecurity threats, including major breaches, active exploits, ransomware, phishing, spyware, and AI security risks.
Foundational
How to Secure Business Communications on Public Wi-Fi
Protect sensitive business communications on public Wi-Fi with practical security strategies that reduce cyber risks, data breaches, and unauthorized access.
Foundational
CNAME vs. A Record: Understanding the Right DNS Choice
Learn the key differences between CNAME and A records, their uses, limitations, and how to choose the right DNS record for your domain.
Intermediate
Exchange Sever DKIM Troubleshooting for Large Email Message
Learn how to troubleshoot DKIM failures in Exchange Server for large email messages, identify common causes, and restore reliable email authentication.
Comparisons
8 DNS Propagation Checker Features To Look For In 2026
Discover the 8 essential DNS propagation checker features to verify records, monitor global changes, detect errors, and ensure reliable DNS performance in 2026.
Foundational
Email Downtime Detection: From Detection To Faster Recovery
Learn how email downtime detection identifies outages early, speeds up response, and helps organizations restore email services faster with less disruption.
News
Meta AI Hacked, npm Worms Strike, Passkey Attack Hijacks – Cybersecurity News [August 03, 2026]
Explore the top cybersecurity threats of the week, from AI breaches and npm worms to passkey attacks, critical flaws, ransomware, and major data breaches.
Tutorials
9 Backup and Recovery Tips Before Public Folder Migration
Discover 9 backup and recovery tips before public folder migration to protect data, reduce risks, ensure smooth recovery, and achieve a successful migration.
Foundational
What Is Piggybacking in Cybersecurity? Types, Risks, Real-World Examples, and Prevention
Learn what piggybacking in cybersecurity means, its types, risks, real-world examples, and prevention strategies to protect against unauthorized access.
Intermediate
How to Audit Your Email Deliverability Before Launching a Campaign
Audit your email deliverability before launching a campaign to improve inbox placement, avoid spam filters, and maximize open rates and engagement.
Foundational
GDPR Consent Emails For B2B Marketing What You Need To Know
Learn what GDPR consent emails for B2B marketing require, how to stay compliant, avoid common mistakes, and build trust while improving email engagement.
News
Iran Hits Infrastructure, EY Data Leak, CRPx0 Breaches Hyundai – Cybersecurity News [July 27, 2026]
Stay updated on the latest cybersecurity threats, ransomware attacks, AI-powered hacking, critical vulnerabilities, and email security best practices.
Tutorials
Why Emails Get Queued: 10 Common Causes And How To Fix Them
Emails get queued due to server issues, authentication errors, and delivery delays. Learn 10 common causes and effective fixes to improve email delivery.
Foundational
No DMARC Record Found: What It Means, Why It Matters, and How to Fix It
No DMARC record found? Learn what it means, why it puts your domain at risk, and how to create, verify, and manage a DMARC record to stop spoofing.
Intermediate
Session Hijacking Via Email Attack Methods And Warning Signs
Learn common session hijacking via email attack methods, warning signs, and practical tips to detect threats early and protect your accounts from attackers.
Intermediate
9 Ways AI and Automation Improve Email Queue Management
Discover 9 ways AI and automation improve email queue management by reducing delays, prioritizing messages, optimizing delivery, and boosting email performance.
News
Cl0p Mass Extortion, Anubis Hits Fairlife, AI Hacks Benchmark – Cybersecurity News [July 20, 2026]
Stay updated with July 2026 cybersecurity news covering Cl0p ransomware, Anubis attacks, AI security breaches, zero-days, data leaks, and emerging threats.
Intermediate
How OAuth 2.0 Is Changing SMTP Relay Authentication
Learn how OAuth 2.0 is transforming SMTP relay authentication with secure, token-based access, stronger email security, and reduced reliance on passwords.
Foundational
Honey Trap Scams: How Cybercriminals Exploit Trust and How to Avoid Them
Learn how honey trap scams exploit trust through romance and social engineering. Discover warning signs, prevention tips, and ways to protect your data and money.
Guides
8 Steps To Recover From A Spam Trap Hit Without Losing Deliverability
Recover from a spam trap hit with these 8 proven steps to restore sender reputation, improve email deliverability, and prevent future blacklist issues.
Guides
How to Recover from a Spam Trap Hit in 8 Simple Steps
Recover from a spam trap hit with these 8 proven steps to restore sender reputation, improve email deliverability, and prevent future blacklist issues.
Intermediate
Why Email Authentication Alone Doesn't Stop Gmail Threats
Email authentication helps verify senders, but Gmail threats can still exploit compromised accounts, malicious links, and social engineering to reach inboxes.
Guides
Common PCI DSS Email Security Audit Findings And How To Avoid Them
Learn the most common PCI DSS email security audit findings and discover practical steps to avoid compliance issues, protect data and strengthen email security.
Tutorials
7 Steps To Verify ARC Seals Using Popular Email Header Analysis Tools
Learn 7 simple steps to verify ARC seals using popular email header analysis tools to validate authentication chains and improve email deliverability.
News
Ecopetrol Theft, Lidl Vendor Incident, Patch Tuesday – Cyber News
Stay ahead of cyber threats with this week's top security news, from ransomware and data breaches to zero-days, plus why SPF, DKIM, and DMARC remain essential.
Intermediate
Proven Methods for Corporate Email Cybersecurity Setup
Strengthen corporate email cybersecurity with SPF, DKIM, DMARC, TLS, and monitoring to prevent spoofing, improve deliverability, and protect your brand.
Foundational
How Microsoft 365 Accounts Become Targets For Credential Harvesting Attacks
Learn how Microsoft 365 accounts become targets for credential harvesting attacks, common tactics used by cybercriminals, and best practices to stay protected.
Advanced
9 SMTP Authentication Hardening Techniques To Protect Mail Servers From Abuse
Strengthen email security with these 9 SMTP authentication hardening techniques to protect mail servers from abuse, spam, phishing, and unauthorized access.
Foundational
What Is Ping Spoofing? Understanding How It Works and How to Prevent It
Learn what ping spoofing is, how attackers use ICMP spoofing, the risks it creates, and practical steps to detect and prevent network security threats.
Intermediate
Common Email Throttling Mistakes That Lead to Deferred or Rejected Emails
Avoid common email throttling mistakes that cause deferred or rejected emails. Learn proven strategies to improve email deliverability and sending success.
News
Accenture Breach, AssuranceAmerica Exposed, Mount Royal – Cyber News
Weekly cybersecurity roundup: Accenture breach, AssuranceAmerica leak, AI ransomware, Edge flaw, ShareFile alert, and key email security updates.
Guides
Public Folder Migration Checklist For Microsoft 365 And Exchange Online
Follow this Public Folder Migration Checklist for Microsoft 365 and Exchange Online to ensure secure, seamless migration with minimal downtime and data loss.
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