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Fix iRedMail by identifying the failing direction first—Internet delivery in, authenticated submission out, or mailbox retrieval—then matching one controlled test to the exact Postfix, Dovecot, Amavisd and DNS evidence. A webmail login alone does not prove that SMTP delivery or IMAP access works. On Ubuntu, the decisive evidence is normally in /var/log/mail.log, /var/log/mail.err, /var/log/mail.warn and the Dovecot logs under /var/log/dovecot/.
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Classify the failure before changing configuration
Do not start by editing main.cf or changing authentication policy. Send one test message in each direction, note the exact time, and classify what failed. This prevents a mailbox-access problem from being “fixed” with an unrelated SMTP change.
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Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →| Failure direction | Typical symptom | First evidence to collect | Most likely layer | Safest first action |
|---|---|---|---|---|
| Inbound Internet mail | External senders receive a timeout, refusal or a bounce; no message reaches the server | Remote SMTP error, connection time, DNS results, firewall and listener state | DNS, network path, port 25, Postfix listener | Verify the domain’s MX and the server’s reachable SMTP listener before inspecting mailboxes |
| Outbound submission | Client cannot send, or Postfix accepts the message and leaves it deferred | Submission response, queue ID, recipient server response and preceding Postfix lines | Client TLS/authentication, DNS lookup, transport, remote policy or TLS negotiation | Follow the queue ID in mail.log; a deferred status by itself is not a diagnosis |
| Mailbox retrieval | SMTP reports success but the user cannot see the message, or IMAP/POP login fails | Dovecot authentication and mailbox logs, local-delivery lines, client protocol settings | Dovecot, LMTP, Amavisd hand-off, mailbox path or TLS | Confirm the delivery path and use the full email address as the login name |
Reproduce the problem and capture the evidence
Use a controlled test with a known sender and recipient. Record the UTC or local timestamp, sender, recipient, client used, and whether the message was sent from webmail, an SMTP client or another mail server. Then watch the logs while repeating only that test.
- Watch Postfix in real time: run
sudo tail -f /var/log/mail.log. Keep a second terminal open forsudo tail -f /var/log/mail.errandsudo tail -f /var/log/mail.warn. - Watch Dovecot for mailbox failures: inspect the relevant file under
/var/log/dovecot/, for example withsudo tail -f /var/log/dovecot/*.log. Authentication, IMAP and LMTP messages often appear there rather than in the Postfix log. - Correlate one message: copy the queue ID from the first Postfix line for the test message. Follow every later line with that ID, including the final delivery status and any remote SMTP reply.
- Save the exact error: an SMTP reply, Dovecot authentication message, connection refusal or DNS error is more useful than a client popup such as “sending failed.”
- Repeat in the opposite direction: test an outside sender to an iRedMail mailbox and an iRedMail user to an outside address. This distinguishes an inbound path problem from an outbound policy or transport problem.
Postfix’s increased debug logging can become extremely noisy. If you temporarily raise verbosity, return it to the normal level after collecting the evidence so that later incidents remain readable.
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Check services and listening ports
First confirm that the components are running, then compare their listeners with the protocol the failing test needs. A process can be “active” while listening only on localhost or on the wrong address.
- Check service state with
sudo systemctl status postfix,sudo systemctl status dovecot,sudo systemctl status amavisand the service used by your iRedMail webmail installation. - List TCP listeners with
sudo ss -ltnp. Confirm the expected address, port and owning process; a listener bound only to127.0.0.1cannot accept connections from the Internet. - Inspect the host firewall and any cloud security-group or upstream NAT rule. A local service can be healthy while an edge firewall silently drops its traffic.
| Port | Service and purpose | What it does not replace | Important qualification |
|---|---|---|---|
| 25/TCP | Postfix SMTP for server-to-server delivery | It is not the normal authenticated client-submission port | It must be reachable from other mail servers for Internet mail to arrive |
| 587/TCP | Postfix submission for authenticated end users | It does not receive ordinary Internet mail addressed to your domain | Use STARTTLS and authentication as configured by the server |
| 465/TCP | Implicit-SSL submission when enabled | It does not replace port 25 for inter-server delivery | Use it only when your Postfix submission service is configured for it |
| 143/TCP and 993/TCP | Dovecot IMAP; 143 can upgrade with STARTTLS, 993 uses SSL/TLS | Neither port sends SMTP mail | Choose the client security mode that matches the port |
| 110/TCP and 995/TCP | Dovecot POP3; 110 can upgrade with STARTTLS, 995 uses SSL/TLS | Neither port submits messages | POP downloads mail and may not preserve the mailbox view expected from IMAP |
| 24/TCP | LMTP hand-off for local delivery | It is not an Internet-facing SMTP endpoint | It is normally loopback-only; exposing it externally is unnecessary |
If port 25 is closed externally, changing an IMAP password or webmail setting will not restore inbound delivery. Fix reachability and the Postfix listener first.
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Repair inbound mail: DNS, port 25 and Postfix acceptance
Confirm the domain points to this server
Every hosted mail domain needs a correct A record for the mail host and an MX record that names the host responsible for receiving mail. Query the public DNS view, not only a local resolver cache:
dig +short A mail.example.com
dig +short MX example.comThe MX target must resolve to the server’s reachable address. If the MX points to an old host, an internal address or a name with no A record, outside senders will never reach this iRedMail installation.
Test the public SMTP path
From a network outside the server’s LAN, test whether TCP 25 can be reached. A timeout usually indicates a firewall, security-group, NAT or provider block; a connection refusal usually means the address is reachable but no process is accepting connections. Check ss -ltnp locally and then inspect every network-control layer between the Internet and the host.
Read the receiving transaction
When a remote server connects, Postfix should log the connection, the envelope recipient and a queue ID. If the remote server reports an SMTP rejection, copy the complete code and text. A recipient rejection, relay denial or policy response is different from a connection failure and requires a different fix. Do not treat a missing message in a mailbox as proof that SMTP failed; Postfix may have accepted it and handed it to the filtering or local-delivery chain.
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Repair outbound mail and interpret a deferred queue
Use sudo postqueue -p to list queued messages. A line ending in status=deferred means Postfix has postponed delivery; it does not identify the cause. The destination response and the lines immediately before it do.
DNS lookup failures
Messages such as an inability to resolve the recipient domain’s MX or A record point to resolver or DNS configuration. Check the server’s resolver settings and query the destination domain directly. A temporary lookup failure can clear on its own, while a persistent failure requires correcting DNS or resolver reachability.
Connection timeouts and refusals
A timeout indicates that Postfix cannot complete a TCP connection to the destination. Investigate outbound firewall rules, routing, provider restrictions and the destination host. A refusal means the destination address answered but did not accept SMTP on the attempted port. Neither condition is fixed by changing a user’s IMAP password.
TLS negotiation errors
If the remote server advertises TLS but negotiation fails, retain the complete Postfix TLS error, hostname and certificate details. Check the system clock, certificate chain and TLS policy before weakening security. Do not disable certificate verification as a blind workaround.
Relay and recipient policy responses
Replies stating that relaying is denied, the sender is unauthorised, or the recipient is rejected identify a policy decision. Verify that the client authenticated to the submission service, that the envelope sender is permitted, and that the recipient address is correctly formed. A remote server’s policy rejection may require correcting your server identity or reputation rather than retrying indefinitely.
Inspect one message in detail
After obtaining a queue ID, use sudo postcat -vq QUEUEID to inspect the queued message and headers, replacing QUEUEID with the actual value. Remove or protect personal content before sharing the output. Once the underlying error is corrected, Postfix will normally retry automatically; use sudo postqueue -f only after confirming that the cause is fixed, because forcing a large queue can create unnecessary load.
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Correct server identity and deliverability DNS
The iRedMail DNS guidance treats A and MX records as required for basic mail operation. Reverse DNS, SPF, DKIM and DMARC are optional for transport but highly recommended for a credible, deliverable identity.
Forward and reverse names must agree
Ensure the server’s fully qualified domain name resolves forward to its public address, and that the address’s PTR record resolves back to an appropriate hostname. Check the reverse record with:
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Publish sender-authentication records
- SPF identifies which hosts are authorised to send for the domain.
- DKIM adds a cryptographic signature that receiving systems can verify.
- DMARC tells receivers how to evaluate alignment and what to do when SPF or DKIM fails.
These records do not make an unreachable port 25 work, but their absence can cause remote systems to quarantine or reject otherwise successful SMTP connections.
Fix SMTP, IMAP and POP client settings
Use the complete email address as the username, not only the part before the at-sign. Match each port to its encryption mode exactly; selecting “SSL” on a STARTTLS port or “STARTTLS” on an implicit-SSL port commonly produces an immediate connection or handshake error.
| Client task | Hostname | Port and security | Authentication |
|---|---|---|---|
| Send mail | Your configured submission hostname | 587 with STARTTLS, or 465 with SSL/TLS when enabled | Full email address and mailbox password |
| Read with IMAP | Your configured IMAP hostname | 143 with STARTTLS, or 993 with SSL/TLS | Full email address and mailbox password |
| Download with POP3 | Your configured POP3 hostname | 110 with STARTTLS, or 995 with SSL/TLS | Full email address and mailbox password |
If Dovecot logs Plaintext authentication not allowed without SSL/TLS, enable STARTTLS or SSL/TLS in the client. Do not weaken Dovecot to permit a plaintext password across an unencrypted connection. If the client still fails, compare its hostname with the certificate name and verify that the corresponding listener is bound on the expected address.
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Repair filtering and local delivery
Successful SMTP acceptance does not guarantee that the message is already in the mailbox. iRedMail commonly passes mail through Amavisd before Postfix hands it to Dovecot through LMTP.
Recognise an Amavisd outage
A Postfix error connecting to 127.0.0.1:10024 means the filtering service is not accepting the expected local connection. On Ubuntu or Debian, restart it with:
sudo systemctl restart amavis
sudo systemctl status amavisThen inspect the Amavisd log and repeat a single test message. If the service stops again, capture the reason before repeatedly restarting it; a dependency, permissions error or memory shortage may be killing it.
Check the LMTP hand-off
When Postfix accepts a message but the mailbox remains empty, follow the queue ID through the Amavisd and Dovecot logs. Look for a failed connection to LMTP on port 24, an invalid recipient, a mailbox-path error or a Dovecot permission problem. LMTP is normally loopback-only, so an external port scan is not an appropriate test for it; verify the local listener and the local-delivery log lines instead.
Verify the mailbox path and ownership
Use the Dovecot log to identify the mailbox location and the account involved. A message delivered to a different domain, alias or catch-all can appear “missing” even though local delivery succeeded. Confirm the recipient address exactly, then inspect the mailbox using IMAP or the server-side mailbox tools rather than assuming the webmail index is current.
Account for memory and service stability
Spam and virus scanning consume substantially more memory than a minimal SMTP relay. The iRedMail project states that a low-traffic production mail server with spam and virus scanning enabled requires 4 GB of memory; the project page does not state a year for that figure. On a smaller host, Amavisd or ClamAV may be killed or fail to start, producing repeated 127.0.0.1:10024 errors and delayed local delivery.
Check service status immediately after a failure, review the Amavisd and system logs for out-of-memory messages, and compare available memory with the configured scanning workload. Add memory or reduce the workload only after confirming the cause; disabling filtering removes protection and should not be the default fix.
Apply changes in a reversible order
Use the following order so that each change has a clear test and rollback point:
- Correct the client’s hostname, username, port and TLS mode, then retry one message.
- Correct A and MX records or the server’s HELO name, wait for DNS propagation appropriate to the records’ TTL, and query the public result again.
- Open the required firewall or security-group rule and verify the listener from an external network.
- Restart only the failed service—Postfix, Dovecot or Amavisd—and capture its status and logs immediately afterward.
- Retest with one inbound and one outbound message, correlating each queue ID.
- Flush a corrected queue only after the destination or local-delivery error is gone. Preserve the original log evidence before cleanup.
Client settings and DNS corrections are generally easy to reverse. Changes to Postfix relay restrictions, Dovecot authentication policy or TLS requirements affect every user and should be made only when the logs identify that layer.
Prepare a useful support escalation
If the failure persists, provide a reproducible, sanitised bundle rather than a screenshot of a client popup. Include:
- The affected direction: inbound, outbound or mailbox access.
- Exact timestamps with timezone, sender and recipient domains, and the queue ID.
- The complete SMTP reply or Dovecot/LMTP authentication error.
- Relevant lines from
/var/log/mail.log,/var/log/mail.err,/var/log/mail.warn,/var/log/dovecot/and Amavisd logs. - Public A, MX and reverse-DNS results, plus the hostname used in HELO.
- Listening-port output, firewall or security-group details, Ubuntu version and iRedMail version.
- What changed immediately before the failure and which tests succeeded or failed.
Redact passwords, message bodies, tokens and personal addresses while retaining domains, timestamps, queue IDs and exact error text. This information lets iRedMail support distinguish a network block from a transport, filtering or mailbox problem without requiring unrestricted server access.
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