Resources
Deliverability
Browse Palisade articles and guides in Deliverability.
What is one-click unsubscribe and is it required?
One-click unsubscribe lets recipients opt out in a single click using RFC 8058 headers, and it's required for bulk senders to Gmail and Yahoo.
Jul 15, 2026
What are the best email verification tools?
Email verification tools check whether an address is real and deliverable before you send. Learn what they test and how to choose the right one.
Jul 14, 2026
Why is Microsoft 365 rejecting my email with a 550 5.7.x error?
Microsoft 365 returns 550 5.7.x when your mail fails a policy or authentication check. Fix SPF, DKIM, and DMARC alignment to clear the access-denied bounce.
Jul 14, 2026
What does SMTP error 421 mean and how do I fix it?
SMTP error 421 is a temporary deferral, not a bounce. Fix it by slowing your send rate and authenticating mail with SPF, DKIM, and DMARC before retrying.
Jul 14, 2026
Why do my emails land in Gmail's Promotions tab?
Gmail sorts marketing-style mail into Promotions using content, sender and engagement signals — not spam. Here is how the tabs work and how to reach Primary.
Jul 14, 2026
Why is Yahoo blocking my emails as unauthenticated?
Yahoo blocks unauthenticated mail because SPF, DKIM, or DMARC failed. Fix the 550 5.7.9 'sender is unauthenticated' bounce by authenticating and aligning.
Jul 10, 2026
Why am I not receiving emails? How to troubleshoot
Not receiving emails? Work through spam filters, a full mailbox, forwarding loops, MX records, and blocklists — the fixes that recover missing mail fast.
Jul 9, 2026
Why is my email queued and how do I fix it?
Email stuck on 'Queued'? It means your message is waiting to send, not failed. See what causes it in Gmail and on mail servers — and how to fix each one.
Jul 4, 2026
Why is Gmail rejecting my emails with a 550 error?
Gmail 550 5.7.26 rejections mean your mail fails authentication. See why Google now rejects instead of defers, and the exact fixes to get delivered.
Jul 3, 2026
What Can We Learn from Travis Hazlewood About Email Deliverability?
Travis leads email deliverability at Ortto, bringing five years of cross‑platform experience to keep both platform and customer emails landing in inboxes.
Sep 29, 2025
SVG vs PNG: Unraveling the Best Image Format for Your Success
SVG vs PNG: which format wins for logos, web, and BIMI email branding — file size, scalability, and when to use each.
Aug 9, 2023