ips.backscatterer.orgWhat Backscatterer is
Backscatterer.org, operated by JunkEmailFilter, is a DNSBL at ips.backscatterer.org that tracks mail servers generating backscatter: bounce messages (Non-Delivery Reports) sent to forged sender addresses. When spam arrives with a spoofed From: address and your MTA accepts it before bouncing, the NDR goes to the innocent address holder rather than the actual spammer. Backscatterer targets the servers producing these misdirected bounces. This is distinct from spam-source blocklists like Spamhaus or Barracuda Central: a Backscatterer-only listing indicates a specific MTA configuration problem, not a broader reputation issue.
How to check if your IP is listed on Backscatterer
Query the DNSBL directly with dig using reverse octet notation. For an IP 192.0.2.10:
dig +short 10.2.0.192.ips.backscatterer.orgA response of 127.0.0.2 means the IP is listed. Empty response means not listed. The web lookup form at www.backscatterer.org also confirms the listing status.
Typical bounce message signatures
| Receiving MTA | Bounce string you will see |
|---|---|
Postfix (Backscatterer as reject_rbl_client) | 554 5.7.1 Service unavailable; Client host [X.X.X.X] blocked using ips.backscatterer.org |
| Exim (custom ACL) | 550 X.X.X.X listed at ips.backscatterer.org |
| SpamAssassin scoring | Header X-Spam-Report contains RCVD_IN_BACKSCATTER with a score contribution (typically +1.5 to +3) |
| Sending server log | DSN 5.7.1 with reference to ips.backscatterer.org in the diagnostic-code line |
Common listing causes
| Cause | Detail | Fix pointer |
|---|---|---|
| Accept-then-bounce on invalid recipients | The classic backscatter pattern that gives the list its name: MTA accepts the message, discovers the recipient does not exist, sends an NDR to the spoofed sender | Configure the MTA to reject at RCPT TO time (SMTP 550) with reject_unknown_recipient |
| Aggressive vacation auto-responders | Out-of-office replies fired for any incoming message including spam. The auto-reply goes to a spoofed sender | Restrict auto-responders to previously-known correspondents; use vacation with a filter list |
| Mailing list manager bouncing to spoofed subscribers | Administrative bounce (subscribe/unsubscribe confirmation) sent to a spoofed address that had never subscribed | Verify list membership before sending administrative bounces; use VERP |
| Legacy 2000s-era MTA configuration | Old defaults on Sendmail 8.x, early Postfix, and Exim without modern ACLs. Modern MTAs default to reject-at-RCPT | Update to a supported MTA release and apply modern default configs |
| Forwarders / catch-all relays | The MTA forwards any incoming message to a downstream target that rejects it, generating an NDR to the original spoofed sender | Reject unknown recipients at the front door; do not accept + forward without validation |
MTA configuration to prevent backscatter
| MTA | Configuration directive |
|---|---|
| Postfix | smtpd_recipient_restrictions = reject_unknown_recipient_domain, reject_unauth_destination, reject_unlisted_recipient. Ensures unknown recipients are rejected during SMTP, not accepted and later bounced. |
| Exim | ACL acl_smtp_rcpt with verify = recipient to check recipient existence before accepting the message. |
| Sendmail | FEATURE(access_db) with recipient checks in access.db; alternatively FEATURE(use_ct_file) with a curated list. |
| Microsoft Exchange | Enable Recipient Filtering under Anti-Spam. Turn on Block messages sent to recipients not listed in the Global Address List. |
How to get delisted from Backscatterer
- Confirm the listing. Query
dig +short REVERSED-IP.ips.backscatterer.orgas shown above. Cross-check on the web form atwww.backscatterer.org. - Fix the MTA configuration. Delisting will not stick if the underlying backscatter continues. Configure reject-at-
RCPT TOusing the directives above. Verify with a test message to a non-existent recipient: your MTA should respond with SMTP 550 beforeDATA, not accept and bounce. - Wait for automatic expiry (free). Listings expire automatically after approximately 28 days with no new observed backscatter. This is the recommended path if you have time.
- Or use paid express removal. Backscatterer.org offers a paid removal service through the site (small one-time fee, typically under 50 USD). Only useful if the underlying cause is genuinely fixed; otherwise you will be re-listed.
- Verify removal. Re-query with
dig. An empty response confirms delisting.
Prevention: staying off Backscatterer
- Reject at RCPT TO, never accept-and-bounce. The single most important rule. Modern Postfix, Exim, and Sendmail defaults do this correctly. Legacy configs from the 2000s do not.
- Auto-responders are dangerous. Restrict vacation replies and out-of-office messages to known correspondents. Never blindly reply to any incoming message.
- Use VERP (Variable Envelope Return Path) for mailing list administrative bounces. This ensures bounces route correctly and are not sent to spoofed senders.
- Callback verification for forwarders. If you forward mail, verify the downstream target accepts the recipient before accepting the message yourself.
- Monitor complaint volume. A sudden spike in bounces often precedes a Backscatterer listing.
Related blocklists
| Blocklist | Focus | Impact |
|---|---|---|
| Backscatterer.org | MTA backscatter specifically | Widely queried in SpamAssassin rulesets; some strict MTAs use for connection-time reject |
| SEM-BACKSCATTER (Spam Eating Monkey) | Backscatter, similar coverage to Backscatterer.org | Less widely queried; useful as cross-reference |
| UCEPROTECT levels 2-3 | Escalation lists that include ranges and ASNs | Distinct from Backscatterer; UCEPROTECT lists on different criteria |
| Spamhaus, Barracuda, Anonmails | Spam-source reputation | Not backscatter-specific; a Backscatterer-only listing means your problem is MTA config, not spam sending |
Frequently Asked Questions
What is backscatter and why does it get me listed?
Backscatter is a bounce message sent to a forged sender address. If your MTA accepts spam before checking whether the recipient exists, then bounces to the spoofed MAIL FROM address, that bounce hits an innocent third party. Backscatterer tracks the MTAs generating these bounces. The fix is to reject at RCPT TO during the SMTP session, not accept and bounce afterwards.
How long does Backscatterer delisting take?
Automatic expiry is approximately 28 days with no new observed backscatter. Paid express removal (typically under 50 USD via the Backscatterer.org site) is faster but only worth it if the MTA config is genuinely fixed. Otherwise you will be relisted within days.
Does Backscatterer listing affect Gmail or Outlook delivery?
Not directly. Gmail and Outlook.com do not query Backscatterer as a primary signal. However, SpamAssassin-based filters (used by many corporate mail servers, ISPs, and hosting providers) do, so a listing degrades deliverability specifically to those environments. Backscatterer is more painful for B2B sending than for consumer marketing.
Is Backscatterer operated by UCEPROTECT?
No. Backscatterer.org is operated by JunkEmailFilter (Marc Perkel). UCEPROTECT is a separate operation running uceprotect.net with different lists. The two are frequently confused because both are aggressive, independent blocklists, but they have no shared infrastructure.
Can I use IP rotation to avoid Backscatterer?
IP rotation without fixing the MTA backscatter behavior is treated as evasion and the new IP will be re-listed as soon as it generates backscatter. The fix must be at the MTA config level: reject at RCPT TO, not accept-and-bounce. IP rotation is only meaningful once the underlying config is corrected.
For the full reference catalog, see the email blocklist directory.
About the Author
Alaa · LinkedIn
Email infrastructure specialist with 8+ years of hands-on experience in SMTP, deliverability, and email verification. I’ve configured and troubleshot mail systems across Postfix, Exchange, and cloud relays, managed IP reputation and warmup campaigns, and built verification pipelines processing millions of addresses. My work spans DNS authentication (SPF, DKIM, DMARC, BIMI), bounce handling, blocklist monitoring, and compliance frameworks including CAN-SPAM and GDPR. I write every article on SMTPedia to give email professionals, developers, and marketers the accurate, RFC-grounded reference they need.
About SMTPedia
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