Intermediate
DMARC Adoption Is Rising. Is Protection Keeping Up?
Discover why rising DMARC adoption may not ensure email security. Learn how to prevent domain spoofing and strengthen email authentication.
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 (36)
Advanced
How OEM Anti-Phishing Detects Spoofed Domains And Malicious Email Links
Learn how OEM anti-phishing solutions detect spoofed domains and malicious email links to prevent phishing attacks, protect users and strengthen email security.
Foundational
What Is Emailpond? Email Warmup And Sender Reputation
Discover what Emailpond is, how email warmup works, and how it helps build sender reputation, improve deliverability, and keep emails out of spam folders.
Foundational
What Is URL Manipulation and URL Rewriting? A Complete Guide
Learn how URL manipulation and URL rewriting work, their key differences, common techniques, security risks, and best practices for managing URLs effectively.
Intermediate
The Email Breach Bill Is Bigger Than The Stolen Money
Email breaches cost more than stolen funds, exposing businesses to reputational damage, regulatory fines, recovery expenses, and lasting customer trust issues.
Guides
Yahoo Phishing Report Email: How To Identify And Report Suspicious Messages
Learn how to identify Yahoo phishing emails, spot suspicious messages, and report scams safely to protect your account, personal information and email security.
Tutorials
How To Troubleshoot Zendesk DKIM Configuration Mismatches In DNS
Learn how to troubleshoot Zendesk DKIM configuration mismatches in DNS, fix record errors, verify email authentication, and improve email deliverability.
News
Cisco SD-WAN Vulnerability, Citrix Zero-Days, SharePoint Ransomware Risk – Cybersecurity News [October 05, 2026]
Explore this week’s top cybersecurity news, including zero-day exploits, AI-driven attacks, ransomware threats, phishing campaigns, and major data breaches.
Intermediate
Improving Facility Management CMMS Use For Compliance Outcomes
Learn how facility management CMMS can improve compliance with standardized inspections, corrective actions, preventive maintenance, recordkeeping, and audits.
Guides
Why Gmail Rejects Emails After A Mail Server Migration: SMTP Errors And Fixes
Learn why Gmail rejects emails after a mail server migration and discover SMTP error fixes, DNS updates, and email authentication steps to restore delivery.
Foundational
Shared Email Accounts: Security Risks and How to Avoid Them
Shared email accounts can create security risks such as weak passwords, poor accountability, and unauthorized access. Learn safer ways to secure shared inboxes.
Intermediate
How To Plan An Active Directory Migration Without Disruption
Plan a smooth Active Directory migration with careful preparation, risk management, backups, testing, and step-by-step execution to minimize disruption.
Foundational
Password Threats: How Stolen Credentials Put Business Email At Risk
Password threats can expose stolen credentials, compromise business email, enable account takeovers, and increase the risk of phishing, fraud and data breaches.
Foundational
Can A DNS Audit Detect Unauthorized Email Senders?
A DNS audit can identify unauthorized email senders by reviewing SPF, DKIM, DMARC, and MX records for outdated, misconfigured, or suspicious sending sources.
News
Linux Kernel Vulnerabilities, Critical Authlib Bypass, 500,000 Secrets Exposed – Cybersecurity News [September 28, 2026]
Explore the latest cybersecurity news, from Linux kernel flaws and Apple zero-days to exposed secrets, malware threats, ransomware, and major cyber attacks.
Foundational
Domain Records Lookup: A Guide To DNS And Email Authentication
Learn how domain records lookup works to check DNS, SPF, DKIM, and DMARC records, troubleshoot email authentication issues, and improve email security.
Foundational
From Website To Inbox: How Consistent Brand Messaging Builds Trust In Customer Communications
Discover how consistent brand messaging from website to inbox builds customer trust, strengthens credibility, and delivers a seamless communication experience.
Intermediate
How to Fix SPF Softfail: Domain Does Not Designate IP as Permitted Sender
Learn how to fix SPF softfail errors, identify unauthorized sending IPs, update SPF records, and improve email authentication with SPF, DKIM, and DMARC.
Guides
Online PTR Lookup: How To Check IPV4 And IPV6 Reverse DNS
Check IPv4 and IPv6 reverse DNS with an online PTR lookup. Learn how PTR records work, verify reverse DNS entries, and troubleshoot common lookup issues.
Foundational
Email Sign-Offs That Help Recipients Verify And Act On Business Messages
Discover how effective email sign-offs help recipients verify business messages, build trust, and take the right action with confidence.
Tutorials
Spamexperts Outgoing SPF: How To Configure SPF For Outbound Email
Configure SpamExperts Outgoing SPF to authorize outbound mail servers, improve email delivery, prevent spoofing, and strengthen your domain’s email security.
News
Bitget Crypto Heist, AI Bypasses Controls, NetScaler Flaws Exploited – Cybersecurity News [September 21, 2026]
Catch up on last week’s top cybersecurity news, from major breaches and exploited zero-days to AI phishing, ransomware arrests, and emerging threats.
Tutorials
How To Configure An SPF Record For Rackspace Email
Learn how to configure an SPF record for Rackspace Email, authorize trusted senders, prevent spoofing, improve email security and support better deliverability.
Guides
How to Configure SPF and DKIM for IONOS Email
Learn how to configure SPF and DKIM for IONOS email, including DNS setup, CNAME records, verification steps, common errors, and DMARC considerations.
Foundational
VOIP Spoofing: How It Works And How To Protect Your Business
Learn how VoIP spoofing works, the risks it creates for businesses, and practical ways to detect, prevent, and protect your organization from spoofed calls.
Tutorials
How To Configure Qualtrics SPF: A Step-By-Step Guide To Setting Up Your SPF Record
Configure Qualtrics SPF with this step-by-step guide to authorize email senders, improve deliverability, and protect your domain from spoofing and phishing.
News
ShinyHunters DMV Leak, Cisco Fixes Zero-Day, Cyberattack Ship Tracking – Cybersecurity News [September 14, 2026]
Cybersecurity news roundup covering ShinyHunters, Cisco zero-days, North Korean attacks, AI security breaches, ransomware, and emerging threats.
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.
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.
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