10 Best Blacklist Monitoring Tools for Founders [2026 Updated]

1. MXToolbox

• Type: Paid
• URL: https://mxtoolbox.com
• Overview: MXToolbox provides comprehensive blacklist checks and an IP/Domain blocklist monitoring service that continuously scans dozens of RBLs and sends alerts when listings occur. It includes historical listing logs, delisting guidance, and uptime/SMTP health checks to help troubleshoot deliverability issues quickly.

2. HetrixTools

• Type: Paid
• URL: https://hetrixtools.com
• Overview: HetrixTools offers blacklist monitoring for IPs and domains with hourly checks, stacked notifications, and delisting links, plus public/private blacklist reports and API access. Its platform also integrates with many alert channels (email, SMS, Slack, PagerDuty) so teams can act fast when a listing appears.

3. MultiRBL (multirbl.valli.org)

• Type: Free
• URL: https://multirbl.valli.org
• Overview: MultiRBL is a free multi-DNSBL/RBL lookup tool that checks an IP or domain against a large collection of public blocklists and provides informational details on each match. It’s ideal for ad-hoc investigation to see which specific blacklists are flagging your mail infrastructure.

4. Spamhaus

• Type: Free
• URL: https://www.spamhaus.org
• Overview: Spamhaus operates widely-used blocklists (e.g., SBL, XBL, PBL) and provides lookups and information on why an IP or domain is listed, plus clear delisting procedures. Its lists are a key source for many mail providers and are essential to check for email deliverability and reputation issues.

5. Cisco Talos Intelligence

• Type: Free
• URL: https://www.talosintelligence.com
• Overview: Cisco Talos offers IP and domain reputation lookup tools and threat intelligence used by many security and mail platforms to determine blocking or reputation status. The service provides reputation context and classification, helping marketers and admins identify reputation issues affecting delivery.

6. Barracuda Central (Reputation Lookup)

• Type: Free
• URL: [urlhttps://barracudacentral.org/lookups]https://barracudacentral.org/lookups[/url]
• Overview: Barracuda Central maintains a real-time reputation database for IPs and URLs and provides public lookup tools to see whether an IP or domain is rated poorly or blocked by Barracuda appliances. The lookup includes historical reputation information and guidance for remediation for listed senders.

7. Google Postmaster Tools

• Type: Free
• URL: https://postmaster.google.com
• Overview: Google Postmaster Tools gives domain owners inbox placement metrics, spam rates, and domain/IP reputation insights specific to Gmail, enabling you to detect issues that can lead to blocking or poor deliverability. It’s a must-use for monitoring Gmail-specific reputation and troubleshooting delivery to Google users.

8. Microsoft SNDS (Smart Network Data Services)

• Type: Free
• URL: https://sendersupport.microsoft.com/snds
• Overview: Microsoft SNDS provides senders with data about their IP’s sending reputation within Microsoft’s email ecosystem and visibility into spam complaint rates and other signals that can cause blocking. Use SNDS to monitor and react to reputation changes affecting delivery to Outlook/Hotmail/Exchange Online recipients.

9. SpamCop

• Type: Free
• URL: https://www.spamcop.net
• Overview: SpamCop operates the SpamCop Blocking List (SCBL) and provides tools to lookup IPs and report spam; it also publishes listing details and removal procedures for senders. Monitoring SCBL listings helps reduce the risk of being blocked by networks that rely on SpamCop data.

10. Validity (250ok / Deliverability solutions)

• Type: Paid
• URL: https://www.validity.com
• Overview: Validity’s deliverability products (including technology from 250ok) provide blacklist monitoring, inbox placement, and reputation analytics as part of a broader email deliverability suite for marketers. Their platform centralizes monitoring across multiple blocklists and mailbox providers and gives actionable reports to improve sender reputation.