Home/Fix/Delivery ProblemsDelivery ProblemsTroubleshoot mail that is not delivered, delayed, deferred, or bouncing.Reading time: 8 minDifficulty: IntermediateEstimated duration: 8 minPrerequisites: DeliverabilityLast updated: 2026-07-17Author: EmpirePrerequisitesDeliverabilityWhether mail is accepted and where it is placed — inbox, promotions, spam, or rejected.▼Related learningDeliverabilityWhether mail is accepted and where it is placed — inbox, promotions, spam, or rejected.▼Related problemsDeferred messagesReceivers return temporary SMTP failures (4xx), forcing retries instead of immediate acceptance.Delayed deliveryMail eventually arrives but takes much longer than normal due to greylisting, queues, or throttling.Emails not deliveredMessages never reach the recipient mailbox — rejected, discarded, or stuck without a successful delivery.Hard bouncePermanent delivery failure (typically 5xx) because the address or domain cannot accept mail.Soft bounceTemporary delivery failure that may succeed later — full mailboxes, greylisting, or transient outages.▼Recommended toolsGoogle Postmaster ToolsGoogle’s official dashboard for domain reputation, spam rate, and authentication success at Gmail.MXToolboxPopular DNS and mail diagnostics suite for SPF, DMARC, blacklist, and MX checks.WorkflowsOpen step-by-step: Diagnose mail DNS failuresSeparate authoritative errors, cache staleness, and delegation problems.Open step-by-step: Remove invalid addressesOperationalize ongoing removal of hard bounces, complainers, and known risky addresses.Open step-by-step: Investigate bounce reportsClassify bounce DSNs, find root causes, and feed suppressions or infrastructure fixes.Continue LearningInbox Placement ProblemsDiagnose spam folders, promotions tabs, and missing inbox placement.PreviousDNS & Infrastructure ProblemsNextInbox Placement Problems