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Multi-RBL Lookup

The InteSys Multi-RBL Lookup checks an IP address or domain against over 200 DNS-based blacklists (RBLs/DNSBLs) in real time. It also performs Forward-Confirmed Reverse DNS (FCrDNS) verification. Access it at intesys.io/tools/multirbl.

What It Checks

Blacklist Scanning

The tool queries over 200 public and private DNS-based blacklists simultaneously, including:

  • Spamhaus (SBL, XBL, PBL, DBL)
  • Barracuda (BRBL)
  • SpamCop (BL)
  • SORBS (multiple lists)
  • UCEProtect (Level 1, 2, 3)
  • Composite Blocking List (CBL)
  • And 190+ additional lists

Results stream in real time as each blacklist responds, so you see results immediately without waiting for all queries to complete.

Forward-Confirmed Reverse DNS (FCrDNS)

FCrDNS verifies that your IP address has a proper PTR record and that the PTR hostname resolves back to the same IP. This is a fundamental requirement for email deliverability.

IP 203.0.113.10
  └── PTR → mail.example.com (reverse DNS)
        └── A → 203.0.113.10 (forward DNS - matches!)

FCrDNS Failures

Many mail servers reject email from IPs that fail FCrDNS verification. If your PTR record is missing or does not match, contact your hosting provider (or InteSys support for VPS customers) to configure it correctly.

How to Use

  1. Navigate to intesys.io/tools/multirbl
  2. Enter an IP address (e.g., 203.0.113.10) or domain name
  3. Click Check
  4. Watch results stream in real time as blacklists respond

Understanding Results

Each blacklist returns one of three statuses:

Status Meaning
Not listed Your IP is clean on this blacklist
Listed Your IP is on this blacklist — action required
Timeout The blacklist did not respond (not necessarily a problem)

Result Summary

The tool provides an overall summary:

  • Total blacklists checked
  • Listed count — How many lists your IP appears on
  • Clean count — How many lists returned not-listed
  • FCrDNS status — Pass or fail with details

What to Do If Listed

1. Identify the Cause

Common reasons for blacklisting:

  • Compromised server sending spam
  • Open relay allowing unauthorized email sending
  • Infected device on your network
  • Shared IP where another tenant caused the listing
  • Misconfigured application generating excessive bounces

2. Fix the Root Cause

Before requesting delisting, resolve the underlying issue. Delisting without fixing the problem will result in re-listing.

3. Request Delisting

Each blacklist has its own delisting process:

Blacklist Delisting Method
Spamhaus spamhaus.org/lookup — Self-service removal for most lists
Barracuda barracudacentral.org — Online removal request
SpamCop Automatic removal after 24-48 hours if spam stops
SORBS sorbs.net — Online delisting form
UCEProtect Level 1 Automatic removal after 7 days if spam stops

Monitor Regularly

Check your mail server IPs at least weekly. New listings can appear at any time due to compromised accounts, backscatter, or false positives. Early detection prevents deliverability damage.

Best Practices for Clean IPs

  • Authenticate email — Configure SPF, DKIM, and DMARC for all sending domains
  • Monitor outbound traffic — Watch for unexpected spikes in email volume
  • Secure your server — Keep software updated, disable open relays, use strong passwords
  • Process bounces — Remove invalid addresses to reduce bounce rates
  • Use dedicated IPs — For critical email, use a dedicated IP not shared with other senders