Delivery Problems
Troubleshoot mail that is not delivered, delayed, deferred, or bouncing.
- Reading time:
- 8 min
- Difficulty:
- Intermediate
- Estimated duration:
- 8 min
- Prerequisites:
- Deliverability
- Last updated:
- 2026-07-17
- Author:
- Empire
Prerequisites
Related Learn Articles
Related Problems
- Deferred 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.
Related Toolbox Tools
Related Workflows
- Diagnose mail DNS failuresSeparate authoritative errors, cache staleness, and delegation problems.
- Remove invalid addressesOperationalize ongoing removal of hard bounces, complainers, and known risky addresses.
- Investigate bounce reportsClassify bounce DSNs, find root causes, and feed suppressions or infrastructure fixes.