The Blog

Field notes on deliverability.

Hard-won lessons on email verification, inbox placement, and keeping your sender reputation spotless — from the team that's been verifying email since 2000.

Anti-spam laws and compliance: CAN-SPAM, GDPR, CASL

Email Verification GDPR Legal Basis in 2026

Ensure your email verification complies with GDPR. Learn the legal basis for verifying emails, consent requirements, and how MailTester supports lawful.

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Email blocklists: monitoring, causes and delisting

Why Your IP Got Blocked by Proofpoint: Common Causes

Stop being blocked by Proofpoint. Learn the real reasons your IP was flagged, how to diagnose it, and how verification tools like MailTester help prevent.

Sender reputation, IP warm-up and sending infrastructure

Preference Center to Reduce Complaints in 2026

Lower email complaints with a smart preference center. Clean your list, control frequency, and improve deliverability using real-time verification and.

Sender reputation, IP warm-up and sending infrastructure

How Email Deliverability Affects Creator Platform Reputation

Learn how deliverability impacts your creator platform reputation. Reduce bounces, avoid spam filters, and keep your audience engaged with real inbox.

Email authentication: SPF, DKIM, DMARC, BIMI and MTA-STS

SPF Flattening Manual vs Automated Dynamic Services in 2026

Compare manual SPF flattening with dynamic automated services. Reduce bounces, improve deliverability, and fix email delivery issues with real tools and.

Bounce codes and SMTP errors explained

Azure Outbound SMTP Port 25 Restriction and Exception Process

Fix Azure outbound SMTP port 25 restriction with the official exception process. Learn how to verify email addresses and prevent delivery failures in your.

Email deliverability fundamentals and best practices

How to Delegate Subdomain for Email Sending to Third-Party Vendors

Learn how to safely delegate a subdomain for email sending to third-party vendors. Prevent deliverability issues with proper setup and verification.

Inbox placement by mailbox provider: Gmail, Outlook, Yahoo and spam filters

Why Gmail Spam Rate Shows No Data in Postmaster Tools

Discover why your Gmail spam rate shows 'no data' in Postmaster Tools and how to verify email list health with accurate, real-time validation.

Inbox placement by mailbox provider: Gmail, Outlook, Yahoo and spam filters

EOP SCL 5 6 versus 9: What Happens to the Message in 2026

Understand how EOP SCL 5, 6, and 9 affect email delivery. Learn what happens to messages at each score level and how to fix issues before they impact.

Email authentication: SPF, DKIM, DMARC, BIMI and MTA-STS

Disabling IPv6 for Outbound Mail on Postfix Exim and Sendmail

Fix email delivery issues by disabling IPv6 in Postfix, Exim, or Sendmail. Learn how to configure inet_protocols for IPv4-only mail flow and improve.

Sender reputation, IP warm-up and sending infrastructure

Why .xyz .top .click TLDs Hurt Email Reputation in 2026

Discover why .xyz, .top, and .click TLDs harm email deliverability. Learn how to verify high-risk domains and protect sender reputation with real-time.

Email authentication: SPF, DKIM, DMARC, BIMI and MTA-STS

DMARC p=reject Broke Our Invoices from Third Party Tool

Stop invoice bounces from third-party tools. Diagnose and fix DMARC p=reject failures with real email verification.

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Occasional, practical notes on verification and inbox placement. No spam — we'd be embarrassed.