Home/Tools/ESPsESPsEmail service providers for transactional and marketing sending.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 toolsSendGridTransactional and marketing email platform with APIs, SMTP, and authentication tooling.MailgunDeveloper-focused email API for transactional sending and inbound routing.Amazon SESHigh-scale cloud email sending with fine-grained infrastructure control on AWS.PostmarkReliable transactional email with strong deliverability defaults and message streams.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 LearningDevelopmentEngineer-oriented SMTP and DNS utilities for debugging mail paths.PreviousAutomationNextDevelopment