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- 15 minutes read
Gmail 550-5.7.26 error: Fix unauthenticated email
Gmail 550-5.7.26 error: Fix unauthenticated email
Learn what Gmail’s 550-5.7.26 “This Mail Is Unauthenticated” bounce means, what triggers it, and how to fix it with SPF, DKIM, and DMARC.
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All blog articles
- 13 minutes read
How to read DMARC reports: Enterprise guidance
Learn how to read DMARC reports, understand what the data means, and reduce manual effort with a clearer, tool-led approach.
- 10 minutes read
Is it safe to open spam emails? Enterprise risks
Is it safe to open spam emails? Usually, yes. Risk escalates with links, attachments, and credential prompts – then containing outbound abuse quickly matters.
- 17 minutes read
Botnet attacks explained: How to reduce risk
A botnet is a network of infected devices used for spam, phishing, and malware. Learn how DMARC enforcement reduces spoofing that abuses your domain.
- 11 minutes read
Use proactive alerts to prevent DMARC failures
Proactive alerts flag DNS changes, new senders, and lookalike domains to prevent DMARC failures, keep critical email flowing, and safeguard users.
- 9 minutes read
PayPal email scam: How it worked before the fix
A recent PayPal email scam used real PayPal messages to show fake purchase details and a callback number. See how it worked.
- 9 minutes read
Reverse DNS mismatch: Fix SMTP banner errors
Fix “reverse DNS does not match SMTP banner” errors by aligning PTR, A records, and server identity to restore trust and reliable email delivery.
- 21 minutes read
Adopt DMARC without an in-house DNS expert
Learn how to adopt and enforce DMARC without an in-house DNS expert. Understand common SPF, DKIM, and DMARC pitfalls, and see how managed services reduce risk.
- 17 minutes read
Email-first cybersecurity predictions for 2026
Explore key cybersecurity predictions for 2026, from AI-powered phishing to DMARC enforcement, BIMI adoption, SPF and DKIM limits, Zero Trust, and automation.
- 21 minutes read
No DMARC record found: Fix this critical mistake
Seeing a “no DMARC record found” error for your domain? Learn what it means, how it exposes you to spoofing and BEC, and how to move safely to p=reject.
- 15 minutes read
TLS 1.2: Why it still matters for secure email
TLS 1.2 remains vital for secure communication. Learn why it’s still widely used, how it compares to TLS 1.3, and how to strengthen your TLS posture.
- 21 minutes read
BEC: Explaining Business Email Compromise
Learn what Business Email Compromise (BEC) is, how to spot common scams, respond to attacks, and use SPF, DKIM, and DMARC to prevent future fraud.
- 10 minutes read
550 5.7.0 local policy violation: Reasons & fixes
Understand the 550 5.7.0 local policy violation error, common causes, and step-by-step fixes to restore email deliverability.
- 19 minutes read
PII in email: Explanation, risks, & protection
Understand what PII is, why email puts it at risk, and how your business can strengthen security to better protect sensitive information.
- 10 minutes read
DMARC bypass: Attack methods & advised solutions
Learn how attackers bypass DMARC by exploiting gaps in SPF, DKIM, and Microsoft, and the steps you can take to stop spoofed email from reaching inboxes.
- 13 minutes read
How to test email campaigns effectively
Learn how to test email campaigns before sending them. Improve deliverability, enhance engagement, and drive conversions.
- 20 minutes read
Spear phishing vs. phishing: Key differences
Learn the difference between spear phishing vs. phishing, how each attack targets your business, and the steps to protect customers, teams, and your domain.
- 20 minutes read
Email spammer bot: Risks and prevention
Learn what an email spammer bot is, how scraping works, and what DMARC does to protect your domain from abuse. Reduce risk and stop automated attacks.
- 9 minutes read
NCSC is retiring Mail Check & Web Check in 2026
The NCSC is retiring Mail Check and Web Check. Learn what the change means, when it takes effect, and why Sendmarc’s platform is the ideal replacement.