The Blog
Hard-won lessons on email verification, inbox placement, and keeping your sender reputation spotless — from the team that's been verifying email since 2000.
Bounce codes and SMTP errors explained
Learn the exact retry window for SMTP 421 deferrals. Avoid wasted sends and reduce bounce rates with proven guidelines and real-time verification using.
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Ensure your cold emails land in inboxes with accurate multipart HTML and fallback text. Verify your list to reduce bounces and improve deliverability.
Stop false positives on receipt emails. Use real-time verification to detect fake invoice scams and improve inbox placement before sending.
Fix SendGrid shared IP deferrals 421 errors with real-time email verification. Reduce bounces, improve inbox placement, and protect sender reputation.
Migrate from another ESP safely with a 100K/day warm-up plan. Reduce bounces, avoid spam traps, and protect sender reputation using real-time verification.
Reduce your spam score from 6 to under 3 with proven deliverability fixes. Clean lists, fix authentication, test inbox placement, and optimize sender.
Discover whether open tracking pixels hurt deliverability. Learn when to disable them, how they impact inbox placement, and how to verify email list.
Discover what a typo spam trap domain is, how it harms deliverability, and how to avoid it with MailTester’s 98.9% accurate email verification.
Protect your main domain’s reputation. Learn how sending cold emails from your primary domain risks inbox placement and delivery.
Ensure compliance and improve deliverability by testing unsubscribe headers before sending. Use MailTester’s inbox placement and verification tools to.
Stop your transactional emails from landing in spam. Learn which words trigger filters and how to fix them with real verification tools and inbox testing.
Ensure your plain text emails comply with unsubscribe requirements and avoid filters. Test deliverability and list hygiene with MailTester’s real-time.
Stay sharp
Occasional, practical notes on verification and inbox placement. No spam — we'd be embarrassed.
