Deliverability guides
High-signal guides and free checkers for SPF, DMARC, List-Unsubscribe, and inbox requirements.
SMTP AUTH Migration Checker
Fix Exchange Online SMTP AUTH Basic Auth failures (535 5.7.3).
SPF Record Checker
Validate SPF syntax, includes, and lookup count. Spot permerror and temperror.
SPF Lookup Limit (10 DNS Lookups)
Why SPF allows at most 10 DNS lookups and how to stay under the limit.
DMARC Checker
Validate policy, alignment, and reporting. Understand none vs quarantine vs reject.
DMARC Policy Explained
What p=none, p=quarantine, and p=reject mean for your domain.
DMARC Quarantine vs Reject
When to use quarantine vs reject and how receivers behave.
DMARC Reporting (rua / ruf)
Aggregate and forensic reports: what they are and how to use them.
List-Unsubscribe Header Checker
One-click unsubscribe compliance for Gmail and major inboxes.
Email Deliverability Checklist
SPF, DKIM, DMARC and headers — aligned to Gmail, Yahoo, Microsoft.
Read-only checks. We don't send email or modify DNS. How we check