Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsWhen iRedMail stops sending or receiving mail, first identify whether the break is on inbound SMTP, outbound delivery, or mailbox access. Send one controlled test in each direction, then correlate its timestamp and queue ID with Postfix, Dovecot, and Amavisd logs. This avoids changing settings based on an unhelpful webmail or mail-client popup.
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On Ubuntu, the fastest path is to verify service state and listening ports, confirm DNS and server identity, and then follow the message through the Postfix–Amavisd–Dovecot chain. Port 25 must be reachable for Internet mail to arrive; port 587 is for authenticated client submission; IMAP and POP retrieve mail but cannot replace SMTP.
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Start with a controlled test and the real error
Do not begin by changing passwords, mail-client ports, or Postfix policy. Reproduce the failure while you can observe the server.
- Send one message from an external account to an iRedMail mailbox.
- Send one message from the iRedMail mailbox to an external account.
- If users can log in but cannot see new mail, send a local test to the same mailbox and record whether SMTP accepts it.
- Write down the exact time, sender, recipient, direction, and any SMTP reply. For a queued message, capture its Postfix queue ID.
On Ubuntu, watch the main mail log during the test:
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sudo tail -F /var/log/mail.logAlso inspect errors and warnings after the attempt:
sudo less /var/log/mail.err
sudo less /var/log/mail.warniRedMail installations commonly write Dovecot events under /var/log/dovecot/*.log. Match the same timestamp and account there. A client message such as “sending failed” is only a symptom; the decisive evidence is the SMTP, LMTP, IMAP, or filter response recorded by the server.
Classify the failure before changing anything
The first decision is the direction and layer of the failure. Different paths use different services and ports, so a fix for one path can leave another untouched.
| What you observe | Path to investigate first | Likely layers |
|---|---|---|
| Mail from outside never connects to the server | Inbound SMTP on port 25 | MX/A DNS, firewall or security group, NAT, provider port blocking, Postfix listener |
| External server connects but its message is rejected | Postfix SMTP acceptance | Recipient response, HELO identity, policy checks, TLS, Postfix configuration |
| Postfix accepts an outbound message and it remains queued | Postfix delivery transport | Destination DNS, connection timeout or refusal, TLS negotiation, relay denial, recipient response |
| SMTP reports success but the message is absent from the mailbox | Filter and local delivery | Amavisd, LMTP, Dovecot, mailbox delivery path |
| Webmail login works but a desktop or phone cannot send | Authenticated submission | Port 587/465, STARTTLS or SSL mode, username format, authentication policy |
| Incoming mail exists but a client cannot read it | IMAP or POP retrieval | Dovecot listener, TLS mode, credentials, network access |
Check service state and listening ports
Confirm that the four relevant components are running before interpreting higher-level errors:
sudo systemctl status postfix
sudo systemctl status dovecot
sudo systemctl status amavisCheck the webmail service using the service name installed on your system. If a unit is inactive, inspect its recent journal entries before restarting it:
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sudo journalctl -u postfix -n 100 --no-pager
sudo journalctl -u dovecot -n 100 --no-pager
sudo journalctl -u amavis -n 100 --no-pagerCompare actual listeners with the expected ports:
sudo ss -ltnp| Port | Service and purpose | What a failure means |
|---|---|---|
| 25 | Postfix SMTP between mail servers | Must be reachable from the Internet for other servers to deliver inbound mail. |
| 587 | Postfix submission for authenticated users | Clients cannot submit mail if this listener or its TLS/authentication policy is unavailable. |
| 465 | Submission over SSL when enabled | Works only when the server is configured for this service and the client uses implicit SSL. |
| 143 | Dovecot IMAP with STARTTLS | Mailbox retrieval requires a reachable listener and a client that upgrades to TLS. |
| 993 | Dovecot IMAP over SSL | Use implicit SSL in the client. |
| 110 | Dovecot POP3 with STARTTLS | Retrieval fails if POP3 is disabled, blocked, or the client does not negotiate TLS. |
| 995 | Dovecot POP3 over SSL | Use implicit SSL in the client. |
| 24 | LMTP, normally loopback-only | Local delivery can fail when the filter or Postfix cannot reach Dovecot’s LMTP endpoint. |
A process listening only on 127.0.0.1 is intentionally local; do not expose LMTP port 24 to the Internet. Conversely, a public SMTP service bound only to loopback cannot receive Internet mail. Check host firewalls, cloud security groups, router/NAT rules, and upstream provider restrictions when a listener exists locally but remote tests time out.
Correct DNS and the server’s identity
For each hosted domain, iRedMail’s DNS guidance requires an A record for the mail host and an MX record directing the domain to that host. An MX record tells other mail servers where to deliver messages; it does not open a firewall port or create a mailbox.
Verify the records from a resolver outside the server’s local network:
dig +short A mail.example.com
dig +short MX example.comThe server’s fully qualified domain name (FQDN) should resolve forward to its public address, and the address should have a matching reverse PTR record. PTR, SPF, DKIM, and DMARC are optional in the basic DNS requirement but highly recommended for a credible sending identity and deliverability. A missing or contradictory identity can produce recipient-side policy failures even when Postfix is functioning.
Postfix’s HELO name must also have a valid A record. iRedMail documents the rejection Helo command rejected: Host not found when the name presented in HELO has no A record. Correct the hostname or DNS record, wait for the record to be visible, and retest; do not suppress the rejection as a workaround.
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When outside senders cannot deliver to iRedMail
1. Confirm that the MX points to the reachable host
Query the recipient domain’s MX record and then query the A or AAAA record of the MX target. If the MX target is an old address, private address, or a name that does not resolve, remote servers will never reach the correct machine. Fix DNS at the authoritative provider before changing Postfix.
2. Prove port 25 reachability
Port 25 is the inter-server SMTP path. A cloud firewall, host firewall, NAT rule, or hosting provider policy can block it even when webmail and port 587 work. Test from a separate network, not only from the mail server itself. A timeout points to routing or filtering; an immediate refusal usually indicates that no process is listening or that a firewall is actively rejecting the connection.
3. Read the inbound SMTP conversation in the log
If a remote server connects, use the Postfix lines at that timestamp to distinguish a DNS/HELO rejection, recipient-policy rejection, TLS problem, or successful acceptance. The remote sender’s SMTP reply and Postfix’s queue ID establish whether the message entered your system. Once accepted, the problem is no longer basic inbound connectivity; follow the queue ID into filtering and local delivery.
4. Trace accepted mail through filtering and delivery
An accepted message that never appears in a mailbox normally requires inspection of Amavisd, LMTP, and Dovecot logs. Check whether the message was handed to LMTP on loopback port 24 and whether Dovecot recorded delivery or an error. Do not assume that successful SMTP acceptance means the message is already visible in IMAP; acceptance and mailbox delivery are separate stages.
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status=deferred is an outcome, not a diagnosis. Find the destination response and the Postfix lines immediately before it. The same status can result from unrelated failures.
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- DNS failure: Postfix cannot resolve the recipient domain or its MX host. Verify resolver operation and the domain’s MX/A records.
- Connection timeout or refusal: The destination may be unreachable, rate-limiting, refusing port 25, or blocked by your network. Compare repeated attempts and the exact remote response.
- TLS negotiation failure: Inspect the TLS error and the destination’s advertised capabilities. Do not infer a certificate problem from a generic deferred status.
- Relay denial or policy rejection: A remote server may reject the sender, HELO identity, IP reputation, or authentication state. Preserve its SMTP code and text.
- Recipient rejection: A malformed, disabled, or policy-blocked recipient is different from a temporary network failure. The SMTP reply determines whether retrying is appropriate.
- Local filter or delivery failure: If the destination was never contacted, inspect Amavisd, LMTP, and Dovecot instead of repeatedly retrying remote delivery.
Use the queue listing to locate the message and then inspect its log record:
sudo postqueue -pKeep the queue ID with every log excerpt. Do not delete deferred mail until you know whether it is a temporary outage, a configuration error, or a message that should be returned to the sender. If you temporarily increase Postfix logging for diagnosis, restore the normal level afterward; Ubuntu’s Postfix guidance warns that verbose logging can become very noisy.
Repair the Amavisd and ClamAV stage
A Postfix error connecting to 127.0.0.1:10024 means Postfix cannot reach Amavisd’s filter listener. On Debian and Ubuntu, restart the service and immediately verify its state and logs:
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sudo systemctl restart amavis
sudo systemctl status amavis
sudo journalctl -u amavis -n 100 --no-pagerCheck the Amavisd logs for startup, socket, permission, and scanner errors. If it stops again, investigate system memory and resource pressure rather than repeatedly restarting it. The iRedMail project specifies 4 GB of memory for a low-traffic production mail server with spam and virus scanning enabled. Low-memory systems may fail to keep Amavisd or ClamAV running, which leaves Postfix accepting or deferring messages without completing the filter handoff.
Once Amavisd remains active and its listener is available, send a new controlled test. Follow the new queue ID; an old deferred message may not immediately demonstrate the repaired path.
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Use secure client settings for submission and retrieval
Log in with the complete email address, not only the part before @. Configure submission and mailbox retrieval independently: SMTP sends mail, while IMAP or POP downloads it.
| Function | Port | Encryption mode | Authentication detail |
|---|---|---|---|
| SMTP submission | 587 | STARTTLS | Authenticated full email address |
| SMTP submission over SSL | 465 | SSL/TLS when enabled on the server | Authenticated full email address |
| IMAP | 143 | STARTTLS | Full email address and Dovecot password |
| IMAP over SSL | 993 | SSL/TLS | Full email address and Dovecot password |
| POP3 | 110 | STARTTLS | Full email address and Dovecot password |
| POP3 over SSL | 995 | SSL/TLS | Full email address and Dovecot password |
Do not select “no encryption” merely to make a connection succeed. If Dovecot logs Plaintext authentication not allowed without SSL/TLS, enable STARTTLS or SSL/TLS in the client and retry. Weakening Dovecot’s plaintext-authentication policy exposes credentials and treats the symptom rather than fixing the client configuration.
When SMTP works but the mailbox stays empty
Separate the acceptance event from final delivery. A successful SMTP response means Postfix accepted responsibility; it does not prove that Amavisd passed the message or that Dovecot stored it.
- Use the queue ID and timestamp to confirm that Postfix handed the message to the filter.
- Look for Amavisd acceptance, rejection, or crash messages.
- Check whether Postfix connected to LMTP on loopback port 24 and record the exact LMTP reply.
- Review the matching Dovecot log under
/var/log/dovecot/*.logfor authentication, LMTP, and delivery errors. - After correcting the failing component, send a fresh test and verify the message through IMAP or webmail.
If IMAP or POP cannot connect while webmail displays the mailbox, focus on Dovecot listeners, firewall exposure, and the client’s TLS mode. If IMAP connects but shows no new mail, remain on the local-delivery path instead of changing SMTP submission settings.
Apply fixes in the least risky order
Use this order to avoid introducing a second failure while diagnosing the first:
- Capture evidence: reproduce one inbound and one outbound test, record timestamps, queue IDs, and exact replies.
- Check reachability: verify port 25 for inbound Internet mail and port 587 or 465 for authenticated submission; confirm IMAP or POP ports only when retrieval is affected.
- Check service state: confirm Postfix, Dovecot, Amavisd, and the webmail stack are running and listening where expected.
- Check DNS identity: validate A and MX records, forward and reverse naming, and the HELO hostname; then review SPF, DKIM, and DMARC when delivery is rejected by recipients.
- Follow the message: inspect Postfix, Amavisd, LMTP, and Dovecot in sequence rather than changing all configurations at once.
- Correct client TLS: use the full address as username and enable STARTTLS or SSL/TLS for submission and retrieval.
- Address resource failures: if Amavisd or ClamAV repeatedly exits, resolve memory pressure; a low-traffic production scanner setup requires 4 GB of memory according to the iRedMail project.
- Retest and clean up: send a new controlled message, confirm the expected log trail, and return any temporary debug verbosity to normal.
Use the evidence to choose the remediation path
| Evidence | Primary fault domain | First corrective action | Risk and reversibility |
|---|---|---|---|
| No remote connection to port 25 | Network, firewall, NAT, DNS, or listener | Correct MX/A records and permit port 25 to the Postfix host. | DNS and firewall changes are visible and reversible; mailbox-policy changes are unnecessary. |
| HELO host-not-found rejection | Server identity DNS | Give the HELO FQDN a valid A record or correct the configured hostname. | DNS correction is lower risk than disabling the rejection. |
status=deferred with a remote timeout |
Outbound network or destination | Use the destination response, test DNS, and check egress filtering. | Keep the queue while the temporary condition is investigated. |
Connection refused to 127.0.0.1:10024 |
Amavisd or scanner resources | Restart and inspect Amavisd; investigate memory if it stops again. | Service recovery is reversible; repeated blind retries do not fix the cause. |
| Dovecot plaintext-authentication error | Client encryption mode | Enable STARTTLS or SSL/TLS in the client. | Client-side change preserves server security. |
| SMTP accepted, no mailbox copy | Filter, LMTP, or Dovecot delivery | Trace the queue ID through Amavisd, port 24, and Dovecot logs. | Changing SMTP authentication cannot repair local delivery. |
Prepare a useful escalation report
If the path remains unclear, provide a sanitized, reproducible bundle to an administrator or iRedMail support channel. Include:
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- The affected direction: inbound, outbound, or mailbox access.
- UTC or local timestamps for one failed test and its sender and recipient.
- Postfix queue ID and the exact SMTP or LMTP reply.
- Relevant lines from
/var/log/mail.log,/var/log/mail.err,/var/log/mail.warn, Dovecot logs, and Amavisd logs. - Results for the mail host’s A record, the domain’s MX record, and forward/reverse name resolution.
- Listening-port output and any firewall, security-group, or NAT rule affecting ports 25, 587, 465, 143, 993, 110, 995, or local port 24.
- Whether the message was accepted, deferred, rejected, filtered, or delivered locally.
Remove passwords, message contents, private keys, and unredacted personal addresses before sharing logs. Exact evidence lets support distinguish a DNS correction from a network rule, service outage, authentication mismatch, or local-delivery failure without asking you to guess.
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