Home/Tools/DevelopmentDevelopmentEngineer-oriented SMTP and DNS utilities for debugging mail paths.Reading time: 3 minDifficulty: BeginnerEstimated duration: 3 minPrerequisites: NoneLast updated: July 2026Author: EmpireRelated learningDeliverabilityWhether mail is accepted and where it is placed — inbox, promotions, spam, or rejected.AuthenticationIdentity signals for email: SPF, DKIM, DMARC, and related controls.Related problemsGmail spam folderMail authenticated for your domain is accepted by Gmail but filed to Spam.Domain reputation degradedAuthenticated domain identity is treated as untrusted despite IP changes.Related toolsSwaksSwiss Army Knife for SMTP — scriptable SMTP transaction testing for engineers.digCLI DNS lookup utility for authoritative and recursive inspection of mail-related records.nslookupInteractive DNS lookup utility commonly used for quick MX and TXT checks.WorkflowsOpen step-by-step: Diagnose authentication failuresTrace SPF/DKIM/DMARC failures to a remediable cause.Open step-by-step: Audit multi-domain authenticationReview authentication across a domain portfolio.Open step-by-step: Authenticate a new domainPublish SPF, DKIM, and DMARC for a new sending domain and verify authentication before warmup.Open step-by-step: Recover from Gmail spamExit Gmail Spam using Postmaster signals, authentication fixes, and controlled volume.Open step-by-step: Check authenticationRegularly verify SPF, DKIM, and DMARC alignment and report pipelines.Continue LearningUtilitiesGeneral-purpose helpers for domain ownership and day-to-day operator checks.PreviousESPsNextUtilities