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The reliable way to stop spam on a self-hosted iRedMail server is layered filtering: establish trustworthy DNS identity, reject obvious abuse at the SMTP front door, score message content with Amavisd and SpamAssassin, apply narrowly scoped iRedAPD policy exceptions, and deliver detected spam to Junk instead of silently discarding it. This arrangement blocks abusive connections before they consume queue and CPU resources while preserving a recovery path for false positives.
Do the work in that order. Authentication and DNS problems can make legitimate mail look suspicious, while an overly broad whitelist or an untested port change can bypass protection or interrupt submission.
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How iRedMail’s anti-spam path works
A default iRedMail installation normally invokes SpamAssassin through Amavisd. SpamAssassin is not usually operated as a separate, standalone daemon in this design. Amavisd receives the message from Postfix, invokes the content scanners, and returns a result that can include X-Spam-* headers. SMTP-time controls such as postscreen or Postfix DNSBL checks run earlier, before a message enters the normal queue and before expensive content analysis.
Each layer answers a different question:
- DNS identity: Does the server have coherent forward, reverse and sender-authentication records?
- SMTP gate: Should this connecting host be allowed to continue an SMTP transaction?
- Content scoring: Does the message resemble unsolicited or malicious mail?
- Policy exceptions: Is this sender, address, domain or network explicitly trusted or blocked?
- Mailbox delivery: Where can a user recover a message that was classified as spam?
Removing one layer because another is working creates a blind spot. A DNSBL can reject a known bad network but cannot understand a carefully written phishing message; SpamAssassin can score content but only after the server has accepted and processed it.
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1. Fix DNS identity before tuning spam rules
Mail reputation depends on identity as well as message content. The iRedMail DNS guidance treats the server’s A record and the domain’s MX record as required. It describes reverse PTR, SPF, DKIM and DMARC as highly recommended, and notes that spam filters commonly inspect PTR.
Required records
- A record: Point the mail hostname to the public mail server address.
- MX record: Point the recipient domain to the hostname that accepts mail.
Strongly recommended records
- Reverse PTR: Ask the ISP or hosting provider that controls the public IP to map it back to the mail hostname. This is normally not set in the same DNS panel as your zone.
- SPF: Publish a policy listing the hosts authorized to send for the domain.
- DKIM: Publish the TXT record containing the key generated by Amavisd.
- DMARC: Add a policy after SPF and DKIM are passing and aligned. DMARC is intended to help senders and receivers determine whether a message is legitimately from the stated sender and what to do when it is not.
Do not begin with an enforcement-heavy DMARC policy while SPF and DKIM are still failing or misaligned. A premature p=reject policy can reject legitimate mail from systems you have not yet authorized. Verify each sender source first, then increase enforcement deliberately.
2. Choose the SMTP-time gate: postscreen or a Postfix DNSBL
| Option | Where it acts | Main benefit | Main trade-off |
|---|---|---|---|
| postscreen | SMTP connection/front door | Rejects or delays suspicious clients before normal SMTP processing and queueing; iRedMail’s performance guidance considers it more effective than a pure DNSBL arrangement. | Changes port-25 behavior, requires authenticated submission on 587 or 465, and depends on careful DNSBL querying. |
Postfix DNSBL (reject_rbl_client) |
SMTP recipient restrictions | Simple, explicit list-based rejection that can be added to an existing Postfix policy. | Provides less protocol defense than postscreen; list response codes and rule placement must be correct. |
| Amavisd plus SpamAssassin | Message and content scanning | Scores message characteristics and adds spam headers in the normal iRedMail path. | Consumes CPU and requires log-based diagnosis when headers or scores are missing. |
| iRedAPD lists | Policy stage | Targets one address, a domain, subdomains, an IP or a CIDR network precisely. | A broad allow rule can bypass filtering for many senders; greylisting can delay a legitimate first message. |
| Dovecot Sieve | Mailbox delivery | Moves detected spam to Junk so users can inspect and recover it. | Acts after detection; it does not stop SMTP traffic or reduce connection load. |
3. Enable postscreen for a new or high-volume deployment
iRedMail’s performance guidance says that postscreen and DNSBL checks catch much spam before it is placed in the local mail queue, saving system resources. The iRedMail postscreen procedure enables its supplied postscreen configuration and the DNSBL sites selected by that procedure. Inspect the enabled sites rather than treating every list as interchangeable: providers have different policies, response codes and query limits.
Understand the port change first
With postscreen enabled, port 25 is used by postscreen to accept mail from other mail servers. End users submit through port 587 with TLS or port 465 with SSL. This is a behavioral change, not merely another filter switch. Update desktop clients, mobile clients, application SMTP settings and internal documentation before enforcing it.
Keep authenticated submission separate from server-to-server reception. A user who attempts to send through port 25 may see a timeout, an unexpected greeting or an authentication failure even though the mail server itself is healthy.
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Stage the rollout
- Record the current submission settings used by every legitimate client and application.
- Enable the iRedMail postscreen configuration according to the edition and operating-system instructions for your installation.
- Confirm that port 587/TLS and 465/SSL accept authenticated users before asking users to move away from port 25.
- Watch Postfix and postscreen logs for legitimate server-to-server traffic, challenge behavior and DNSBL responses.
- Only after the logs are clean, make the new submission ports the standard for users.
Use a local caching resolver
Mail services perform many DNS lookups. iRedMail warns that a local caching resolver reduces DNSBL query pressure and that free RBL services can return improper responses when query limits are exceeded. A resolver cache therefore protects both performance and accuracy. If a list suddenly appears to stop working, check resolver behavior and provider limits before assuming that Postfix or postscreen is broken.
4. Use a Postfix DNSBL when postscreen is not suitable
A pure DNSBL setup is the fallback when postscreen cannot be deployed. Add reject_rbl_client entries to smtpd_recipient_restrictions, placing them after reject_unauth_destination. The official iRedMail example uses these services:
reject_unauth_destination,
reject_rbl_client zen.spamhaus.org,
reject_rbl_client b.barracudacentral.org,The exact response-code syntax supplied by a DNSBL matters. Read the list’s current usage instructions and use the form expected by that provider; a syntactically valid-looking entry can still produce incorrect results if the provider requires a particular response code or query format.
Reload Postfix after changing the restriction list, then test both a permitted sender and a deliberately blocked test path. Do not configure the pure reject_rbl_client path alongside postscreen’s DNSBL path without understanding the duplicate checks. Running both can create repeated queries, confusing logs and unexpected rejection behavior.
5. Keep Amavisd and SpamAssassin for content scoring
SMTP gates examine the connecting host and protocol behavior. They do not replace content analysis. In the default iRedMail path, Amavisd calls SpamAssassin and can add spam headers that later delivery rules inspect.
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Know which file controls which component
| Component | Debian/Ubuntu | FreeBSD | Purpose |
|---|---|---|---|
| Amavisd overrides | /etc/amavis/conf.d/50-user |
Platform-specific Amavisd configuration | Controls Amavisd behavior, including diagnostic settings. |
| SpamAssassin rules | /etc/mail/spamassassin/local.cf |
/usr/local/etc/mail/spamassassin/local.cf |
Stores local SpamAssassin settings and rule adjustments. |
Do not put SpamAssassin rules in the Amavisd override file or Amavisd directives in local.cf. Keeping the scopes separate makes later troubleshooting much easier.
Diagnose missing spam headers
Amavisd logs through the Postfix log. If delivered messages lack X-Spam-* headers, inspect that log first and use the official iRedMail troubleshooting guidance. For deeper SpamAssassin diagnostics, enable $sa_debug = 1 in the Amavisd configuration, reproduce the problem with a test message, and then disable verbose debugging when finished so routine logs remain readable.
Do not disable Amavisd, ClamAV or SpamAssassin merely because postscreen is rejecting obvious abuse. The SMTP gate protects queue and CPU resources; the scanners handle message-level signals and malware-related inspection.
6. Use iRedAPD for precise allow, deny and greylisting policy
The iRedAPD amavisd_wblist plugin, managed with wblist_admin.py, supports server-wide, per-domain and per-user exceptions. A target can be:
- A complete address such as
sender@example.net. - A domain such as
@example.net. - A domain and its subdomains using
@.example.net. - A single IP address.
- A CIDR network.
Whitelist the narrowest possible identity
If one trusted address is being misclassified, allow that address rather than the entire domain. If a partner legitimately sends from several known hosts, use the smallest documented IP or CIDR range that covers those hosts. A whole-domain or broad-network allow entry can let unrelated compromised accounts or machines bypass content and reputation checks.
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Keep a record of why each exception exists and review it when the sender changes providers. Remove temporary entries after the delivery problem is fixed.
Understand greylisting defaults
Greylisting is available in iRedAPD 1.7.0 and later. With the documented defaults, a retry arriving sooner than 15 minutes is rejected; a client that successfully completes the triplet is retained for 30 days; an unsuccessful triplet is retained for 2 days.
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Start a new deployment in training mode. Some legitimate companies redeliver immediately from a different server or do not retry in the conventional pattern. Watch the logs, identify those senders, and add targeted exceptions before enabling strict rejection. Greylisting is a useful pressure filter, but its delay is a compatibility trade-off rather than proof that a sender is malicious.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.7. Deliver detected spam to Junk with global Dovecot Sieve
Rejecting every message classified as spam makes a false positive difficult to recover. A global Dovecot Sieve rule gives users a review path by moving detected spam into Junk after scanning.
- Start from the sample global Sieve file supplied with the iRedMail documentation for your installation.
- Set Dovecot’s
sieve_beforesetting to the path of that file so it runs before per-user filters. - Ensure the file is owned by
vmail:vmail. - Set its permission to
0500. - Restart Dovecot.
- Send a controlled test message that receives spam headers and confirm that it arrives in the user’s Junk folder.
Sieve does not reduce SMTP connections or queue growth; it is a delivery safety net. Keep SMTP-time rejection for high-confidence connection abuse and use Junk for messages that require a classifier decision.
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8. A safe implementation sequence
- Inventory the installation: Record the operating system, iRedMail edition, mail hostname, public IP, domains, client submission ports and current Postfix, Amavisd, SpamAssassin, iRedAPD and Dovecot settings.
- Establish identity: Create A and MX records, request reverse PTR, publish SPF, publish the Amavisd-generated DKIM key, and add DMARC only after SPF and DKIM pass.
- Prepare DNS caching: Run a local caching resolver and verify that normal DNS and DNSBL lookups resolve consistently.
- Pick one SMTP gate: Prefer postscreen for a new deployment when the port migration is acceptable. Otherwise use carefully placed Postfix DNSBL restrictions.
- Move users to authenticated submission: With postscreen, configure port 587/TLS or 465/SSL for users and reserve port 25 for other mail servers.
- Verify content scanning: Confirm that Amavisd invokes SpamAssassin and that test messages receive expected headers. Use the correct platform files and logs.
- Add policy exceptions: Use iRedAPD lists for the smallest address, domain, IP or CIDR scope that fixes a known false positive.
- Train greylisting: Observe retries in training mode, whitelist incompatible legitimate senders, then enable strict behavior if the logs support it.
- Provide recovery: Configure the global Dovecot Sieve rule, ownership and permissions, restart Dovecot, and verify Junk delivery.
- Measure by symptoms: Review rejection logs, queue volume, spam headers, user reports and Junk-folder recoveries before tightening any rule.
9. Troubleshooting by symptom
Legitimate mail is rejected before delivery
- Check whether postscreen or a DNSBL rejected the connecting IP.
- Verify the sender’s reverse PTR and authentication alignment.
- Confirm that a DNSBL response was genuine and not a query-limit error.
- Add a narrow iRedAPD exception only after identifying the exact address, host or network involved.
Users cannot send after postscreen is enabled
- Confirm that the client uses 587 with TLS or 465 with SSL.
- Check that authentication is enabled on the submission service.
- Make sure the client is not still pointed at port 25.
- Review the postscreen and submission logs separately so a server-to-server rejection is not confused with a client-authentication problem.
Spam reaches the inbox without spam headers
- Inspect the Postfix log for Amavisd processing.
- Verify that SpamAssassin rules are in the platform-correct
local.cfpath. - Temporarily enable
$sa_debug = 1in Amavisd, reproduce the issue, and inspect the resulting diagnostics. - Confirm that a later delivery rule is not removing headers or overriding the destination.
Messages are delayed for 15 minutes
This is consistent with the documented iRedAPD greylisting retry-block default. Check whether the sender retries successfully, whether the successful triplet is retained, and whether the sender’s infrastructure needs a targeted whitelist.
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Use the global Sieve Junk route rather than silent rejection when users need recovery. Verify the sieve_before path, vmail:vmail ownership, 0500 permission and Dovecot restart.
10. Common mistakes to avoid
- Using port 25 for users after enabling postscreen: reserve it for other mail servers and migrate clients to authenticated submission.
- Running duplicate DNSBL paths blindly: understand whether postscreen already performs the checks before adding Postfix
reject_rbl_cliententries. - Ignoring resolver limits: DNSBL providers can impose query limits; a local cache reduces pressure and improper responses.
- Whitelisting an entire provider unnecessarily: broad domains and CIDR ranges bypass protection for more senders than intended.
- Enabling strict greylisting immediately: train first and account for senders with unusual retry behavior.
- Publishing DMARC enforcement before SPF and DKIM work: alignment failures can block legitimate messages.
- Disabling content scanners after adding an SMTP gate: connection reputation and message content are different signals.
- Discarding spam with no review path: route uncertain classifications to Junk so users can recover false positives.
Edition and maintenance notes
The open-source iRedMail product includes SpamAssassin, ClamAV, SPF, DKIM, greylisting, whitelisting, blacklisting and SQL quarantine. iRedMail Enterprise Edition v1.8.4 was listed on September 10, 2026, and adds web-managed greylisting, lists, spam policy and quarantine with per-domain and per-user anti-spam settings. The edition changes how policy is administered, but the underlying operational principles remain the same: establish identity, filter early, score content, scope exceptions narrowly and preserve a recovery path.
There is no published spam-reduction percentage or false-positive benchmark in the cited official iRedMail material. Treat tuning as an operational feedback loop based on your own rejection logs, queue behavior, headers and user reports rather than promising a fixed percentage improvement.
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