Postfix Troubleshooting
Structured diagnostics and recovery guidance for common production incidents.
SMTP Connection Refused
Check listener bindings, firewall policy, service health and network path.
Relay Access Denied
Validate recipient classification, relay restrictions, authentication and transport routing.
SASL Authentication Failed
Inspect mechanism availability, socket paths, credentials, TLS policy and Dovecot/Cyrus logs.
TLS Handshake Failed
Check certificate chain, protocol compatibility, SNI, permissions and policy maps.
Mail Forwarding Loop
Trace Received headers, aliases, transports, virtual maps and relay routes.
Queue Growing Rapidly
Identify affected destinations, SMTP responses, disk latency, DNS failures and policy changes.
Deferred Due to DNS
Verify resolver health, MX/A/AAAA records, DNSSEC failures and timeout behavior.
Sender Address Rejected
Review restriction order, access maps, sender verification and local domain classification.
Recipient Address Rejected
Review destination classes, virtual maps, mailbox existence checks and relay policy.
OpenDKIM Not Signing
Validate milter reachability, table matches, trusted hosts, permissions and DNS selector records.
Dovecot Auth Socket Missing
Check socket path, chroot namespace, service ownership and Dovecot startup errors.
postfix check Errors
Resolve ownership, mode, map, directory and syntax findings before reload.
Mail Stuck in Active Queue
Inspect qmgr limits, transport process health, destination concurrency and filesystem latency.
TLS Private Key Permission Error
Set secure readable ownership for Postfix while avoiding world-readable private keys.
Submission Port Not Listening
Check master.cf syntax, service enablement, firewall rules and process startup logs.
Wrong Outbound Source IP
Inspect smtp_bind_address, transport overrides, multi-instance routing and OS route selection.
HELO or Hostname Mismatch
Align myhostname, smtp_helo_name, PTR and forward DNS for each outbound identity.
Map Changes Not Applied
Rebuild hash/db maps, verify lookup type/path and reload the correct instance.
High Memory Usage
Inspect process limits, active queue size, content filters, concurrency and abnormal clients.
Duplicate Delivery
Trace queue IDs, retries, downstream acknowledgments, application injection and alias expansion.