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.

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

Why Sandbox Emails Don't Reflect True Inbox Placement Rates

Sandbox emails fail to predict real inbox delivery. Learn why and how real inbox placement testing with MailTester gives you honest results for your.

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Email verification and list hygiene for deliverability

How to Split a Shared Domain into Subdomains for Each Unit

Learn how to split a shared domain into subdomains for each business unit with email verification.

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

SPF hardfail -all Bouncing Forwarded Mail: Why It Happens

Why SPF hardfail -all causes forwarded emails to bounce. Fix it with accurate email verification and domain alignment.

Email deliverability fundamentals and best practices

How to Analyze Email Deliverability Postmortems for Long-Term Improvement

Learn how to conduct a thorough email deliverability postmortem to identify root causes, reduce bounces, and improve inbox placement over time.

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

Brazilian ISP Bounce Messages Translated and Explained

Decode Portuguese bounce messages from Brazilian ISPs. Learn what invalid, catch-all, and greylisted codes mean—and how to fix them with real-time email.

Sender reputation, IP warm-up and sending infrastructure

Steps to Retire a Sending Subdomain Without Harming Sender Reputation

Learn the exact steps to retire a sending subdomain safely. Avoid reputation damage, prevent bounces, and protect deliverability with proven methods.

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

Does the 102KB Limit Include Images or Just HTML? | 2026

Discover whether the 102KB email size limit includes images or only HTML. Learn how Gmail and other clients calculate size, avoid clipping, and test inbox.

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

When Strict DMARC Alignment Breaks Third-Party Senders

Fix email deliverability when strict DMARC alignment blocks third-party senders. Learn the root causes and how to verify your list without breaking.

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

Securing Email Infrastructure with Auditable DNS Changes via Version Control

Ensure email deliverability by auditing DNS changes through version control. Prevent misconfigurations and improve sender reputation with traceable.

Bounce codes and SMTP errors explained

Reducing Risk of Email Bounce Rates During Upstream Provider Downtime

Minimize email bounces during upstream provider outages with real-time verification, bulk checks, and inbox-placement testing.

Bounce codes and SMTP errors explained

Brevo SMTP Relay vs Amazon SES: A 2026 Comparison

Compare Brevo SMTP relay and Amazon SES for email delivery. Discover which tool offers better deliverability, cost efficiency, and list hygiene in 2026.

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

Remove Outdated App Passwords in Google Workspace for Compliance

Secure your Google Workspace by identifying and removing outdated app passwords. Ensure compliance, reduce breach risk, and improve account hygiene with.

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