# SenderReputation.org
> Free tools and educational resources for email deliverability. Check sender reputation, validate email authentication records, scan blacklists, and learn how to improve inbox placement. No signup required, no account needed, privacy-focused.
SenderReputation.org is a comprehensive resource for email senders who need to diagnose, monitor, and improve their email deliverability. The site offers professional-grade diagnostic tools, in-depth educational guides, an 80+ term glossary, a bounce code reference database, and a blog covering the latest in email authentication and reputation management. All tools are free and work by querying publicly available DNS data.
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## Tools
### Sender Reputation Checker
URL: https://senderreputation.org/tools/sender-reputation-checker
The flagship tool. Enter any domain to receive a comprehensive Sender Reputation Score graded A through F (0-100 scale). The score is calculated across four weighted categories:
- **Authentication (30%)**: SPF, DKIM, and DMARC record presence, validity, and configuration strength.
- **Blacklist Status (30%)**: Whether the domain or associated IP addresses appear on major DNS-based blacklists.
- **DNS Health (20%)**: MX record configuration, reverse DNS (PTR) records, and overall DNS infrastructure.
- **Infrastructure (20%)**: Mail server responsiveness, TLS support, and sending infrastructure quality.
Grade scale: A (90-100 Excellent), B (75-89 Good), C (60-74 Fair), D (40-59 Poor), F (0-39 Critical).
### Blacklist Checker
URL: https://senderreputation.org/tools/blacklist-checker
Scans a domain or IP address against 10+ of the most widely used and impactful DNS-based blacklists. These are the blacklists that matter most for email deliverability - a listing on any of these will cause significant delivery problems with major mailbox providers like Gmail, Yahoo, Microsoft, and most corporate mail systems.
Blacklists checked include:
- **Spamhaus ZEN** (zen.spamhaus.org) - The most influential blacklist, combining SBL, XBL, and PBL.
- **Barracuda** (b.barracudacentral.org) - Used by organizations running Barracuda email security appliances.
- **SpamCop** (bl.spamcop.net) - Complaint-driven blacklist based on user spam reports.
- **SORBS** (dnsbl.sorbs.net) - Spam and Open Relay Blocking System (decommissioned in 2024, but still queried by some legacy configurations).
- **SORBS Spam** (spam.dnsbl.sorbs.net) - SORBS sub-list (decommissioned).
- **Mailspike** (bl.mailspike.net) - Reputation-based blacklist.
- **PSBL** (psbl.surriel.com) - Passive Spam Block List.
- **UCEPROTECT Level 1** (dnsbl-1.uceprotect.net) - Individual IP listings.
- **WPBL** (db.wpbl.info) - Weighted Private Block List.
- **CBL / Abuseat** (cbl.abuseat.org) - Composite Blocking List for compromised hosts.
- **DroneBL** (dnsbl.dronebl.org) - Lists IPs of exploited/compromised systems.
- **0spam** (bl.0spam.org) - Zero spam tolerance list.
Results show pass/fail status for each blacklist with the specific DNS response code when listed.
### SPF Record Checker
URL: https://senderreputation.org/tools/spf-checker
Validates SPF (Sender Policy Framework) records. Checks for:
- Record presence and proper DNS TXT publication
- Syntax validity and mechanism parsing
- DNS lookup count (must not exceed 10 per RFC 7208)
- Common misconfigurations (multiple SPF records, deprecated ptr mechanism, overly permissive +all)
- Include chain resolution
### DKIM Record Checker
URL: https://senderreputation.org/tools/dkim-checker
Verifies DKIM (DomainKeys Identified Mail) records. Requires a domain and DKIM selector. Checks for:
- Key publication at the correct DNS location
- Key format and encoding validity
- Encryption strength (RSA key length)
- Proper DNS TXT record formatting
### DMARC Record Checker
URL: https://senderreputation.org/tools/dmarc-checker
Checks DMARC (Domain-based Message Authentication, Reporting, and Conformance) records. Validates:
- Record presence at _dmarc subdomain
- Policy setting (none, quarantine, reject)
- Subdomain policy (sp tag)
- Alignment settings for SPF and DKIM (relaxed vs strict)
- Reporting configuration (rua and ruf addresses)
- Percentage tag and other optional directives
### Email Header Analyzer
URL: https://senderreputation.org/tools/header-analyzer
Parses raw email headers to trace the delivery path of an email message. Paste raw email headers to see:
- Complete hop-by-hop delivery chain with timestamps
- Authentication results (SPF, DKIM, DMARC pass/fail)
- Delays between mail servers
- Sender and recipient information
- Mail server software and routing details
### MX Lookup
URL: https://senderreputation.org/tools/mx-lookup
Looks up Mail Exchange (MX) DNS records for any domain. Shows:
- All MX records with priority values
- Mail server hostnames and resolved IP addresses
- TTL values
- Common mail provider identification (Google Workspace, Microsoft 365, etc.)
### Reverse DNS Checker
URL: https://senderreputation.org/tools/reverse-dns-checker
Verifies PTR (pointer) records for IP addresses. Proper reverse DNS is required by many receiving mail servers. Checks:
- PTR record existence for sending IPs
- Forward-confirmed reverse DNS (FCrDNS) - whether the PTR hostname resolves back to the original IP
- Hostname formatting and naming conventions
### SPF Record Generator
URL: https://senderreputation.org/tools/spf-generator
Interactive tool to build valid SPF records. Guides users through:
- Adding authorized IP addresses and ranges
- Including third-party senders (ESPs, CRMs)
- Setting the appropriate qualifier (~all vs -all)
- Keeping within the 10 DNS lookup limit
### DMARC Record Generator
URL: https://senderreputation.org/tools/dmarc-generator
Interactive tool to generate DMARC TXT records. Helps configure:
- Policy level (none for monitoring, quarantine, or reject)
- Subdomain policy
- Aggregate report (rua) destination
- Forensic report (ruf) destination
- Alignment mode for SPF and DKIM
- Percentage of messages to apply policy to
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## Embed These Tools on Your Own Website (Free Widget)
URL: https://senderreputation.org/widget/
Every tool listed above can be embedded on any website with a single script tag. It is free, with no signup, no API key, no monthly cost, and no limit on how many pages you put it on. It exists for site owners who would rather give their own audience a working deliverability tool on the page than send them somewhere else to find one.
### Who embeds it
SaaS and email platform help centers, web hosting and domain registrar support pages, email marketing agency sites, IT and MSP resource pages, deliverability consultants, developer documentation, status pages, and anyone writing about email authentication who wants a live tool sitting next to the explanation.
### Install
Paste this where the widget should appear. It renders inline with your content and resizes itself to fit.
```html
```
That single line gives visitors all nine tools with a dropdown to switch between them: the Sender Reputation Checker, SPF, DKIM, DMARC, Blacklist, MX and Reverse DNS checkers, plus the searchable Bounce Code and Glossary references.
Platform notes:
- WordPress: a Custom HTML block, or directly in a theme template.
- Webflow, Squarespace, Wix, Ghost, Shopify: an Embed or Custom Code block.
- Next.js and React: the framework's script component pointed at the same URL.
- Hugo, Jekyll, Astro, Eleventy, plain HTML: paste straight into the page.
### Options
All are optional attributes on the script tag.
- **data-tools** - Comma-separated list limiting which tools appear: reputation, spf, dkim, dmarc, blacklist, mx, rdns, bounce-codes, glossary. A single value pins the widget to that one tool and hides the menu. Omit for all nine.
- **data-tool** - Which tool opens first when several are available.
- **data-theme** - light, dark, or auto. Auto follows the visitor's system color setting and updates live if they change it.
- **data-domain** - Pre-fills the input with a domain or IP address.
- **data-autorun** - Set to true to run the check on load using data-domain, so the visitor arrives at a finished result with nothing to click.
- **data-width**, **data-max-width**, **data-max-height** - Constrain the widget's size to suit your layout.
### Examples
An SPF checker pinned to one tool, in dark mode, for a blog post about SPF:
```html
```
A searchable bounce code reference for a support or documentation page:
```html
```
A status or onboarding page that checks a known domain automatically on load:
```html
```
### Which tool suits which page
- A guide or blog post explaining SPF, DKIM or DMARC: pin the matching checker so readers can test their own domain as they read.
- A help center or support article: the bounce code lookup, so a customer can decode an SMTP error without leaving your site.
- A glossary or learning resource: the deliverability glossary.
- Setup, onboarding or migration docs: the reputation checker with data-domain pre-filled.
- A hosting or registrar control panel help page: the MX lookup or reverse DNS checker.
### Good to know
The widget is responsive and works on mobile. Visitors never need an account. It follows your chosen theme, or the visitor's system preference by default. A small "Powered by SenderReputation.org" credit line appears with it.
### Common questions this answers
- How do I add an SPF, DKIM or DMARC checker to my website?
- Is there a free embeddable email deliverability tool?
- How do I put a blacklist checker on my WordPress site?
- Can I embed an SMTP bounce code lookup in my help center?
- Is there an email authentication widget with no signup and no API key?
- How do I let my readers check their sender reputation without leaving my site?
The visual embed code generator, full option reference and live preview are at https://senderreputation.org/widget/
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## Guides
### What is Sender Reputation?
URL: https://senderreputation.org/guides/what-is-sender-reputation
Reading time: 12 minutes | Level: Beginner
Covers the fundamentals of sender reputation: what it is, why it matters, and the factors that ISPs and mailbox providers use to evaluate senders. Topics include IP reputation vs domain reputation, how reputation scores are calculated, the role of engagement metrics, and how reputation affects inbox placement.
### Email Authentication Guide
URL: https://senderreputation.org/guides/email-authentication-guide
Reading time: 18 minutes | Level: Intermediate
A complete walkthrough of the three pillars of email authentication:
- **SPF**: How it works, syntax reference, mechanism types, the 10-lookup limit, and common mistakes.
- **DKIM**: Public/private key signing, selector configuration, key rotation, and troubleshooting.
- **DMARC**: Policy options, alignment modes, reporting setup, and a recommended rollout strategy (none -> quarantine -> reject).
### Blacklist Removal Guide
URL: https://senderreputation.org/guides/blacklist-removal-guide
Reading time: 14 minutes | Level: Intermediate
Step-by-step guide covering:
1. What email blacklists are and how they work
2. Common reasons for getting blacklisted (spam traps, complaints, high bounce rates, compromised servers, shared IPs, open relays)
3. How to check your blacklist status
4. Major blacklists explained (Spamhaus, Barracuda, SORBS, SpamCop, CBL) with direct links to each blacklist's lookup and removal forms
5. Five-step removal process: identify listings, diagnose cause, fix root cause, request removal, monitor after removal
6. Prevention best practices (list hygiene, authentication, sending practices, infrastructure security)
7. Blacklist severity tiers (high-impact, medium-impact, low-impact) with priority guidance
8. Typical delisting timelines by blacklist
9. When to contact your ESP
10. Post-removal monitoring plan
### Improving Email Deliverability
URL: https://senderreputation.org/guides/improving-email-deliverability
Reading time: 16 minutes | Level: Intermediate
Best practices for maximizing inbox placement rates. Covers list acquisition and hygiene, engagement-based sending, content optimization, infrastructure setup, warming up new IPs and domains, and monitoring deliverability metrics.
### DNS Records for Email
URL: https://senderreputation.org/guides/dns-records-for-email
Reading time: 15 minutes | Level: Intermediate
How to properly configure all DNS record types relevant to email:
- MX records (mail routing)
- SPF records (sender authorization)
- DKIM records (message signing)
- DMARC records (policy and reporting)
- PTR records (reverse DNS)
- A/AAAA records for mail servers
### Understanding Bounce Rates
URL: https://senderreputation.org/guides/understanding-bounce-rates
Reading time: 10 minutes | Level: Beginner
Explains the difference between hard bounces (permanent failures like invalid addresses) and soft bounces (temporary issues like full mailboxes). Covers acceptable bounce rate thresholds, how bounces affect sender reputation, and strategies to reduce bounce rates including list verification and proper bounce handling.
### Email Bounce Codes Reference
URL: https://senderreputation.org/guides/email-bounce-codes-reference
Reading time: 45 minutes | Level: Reference
Comprehensive reference of SMTP reply codes and enhanced status codes, including provider-specific error messages from Gmail, Microsoft/Outlook, Yahoo, and major ESPs.
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## Additional Resources
### Email Deliverability Glossary
URL: https://senderreputation.org/glossary/
Over 80 email deliverability terms defined and explained, organized alphabetically from A to Z. Each term has its own dedicated page with a full explanation. Covers technical terms (SPF, DKIM, DMARC, DNSBL, MTA, MX record, PTR record, SMTP), industry concepts (sender reputation, inbox placement rate, spam trap, feedback loop, bounce rate), and practices (double opt-in, list hygiene, email warm-up, throttling).
### Bounce Code Lookup
URL: https://senderreputation.org/bounce-codes/
Searchable database of 50+ email bounce codes. Includes both standard SMTP 3-digit reply codes (e.g., 421, 450, 550, 554) and enhanced X.Y.Z status codes (e.g., 4.7.0, 5.1.1, 5.7.1). Each code includes the meaning, common causes, and recommended actions. Filterable by hard bounce, soft bounce, SMTP codes, and enhanced codes.
### Blog
URL: https://senderreputation.org/blog/
Articles covering email authentication, deliverability best practices, and industry updates. Posts include:
- Google and Yahoo 2024 Sender Requirements
- SPF Record Syntax Explained
- Why Your Emails Go to Spam
- DMARC Policies Explained
- Email Warm-up Strategy Guide
### About
URL: https://senderreputation.org/about
Information about SenderReputation.org's mission, approach (open/transparent, no account required, privacy-focused, free forever), the full list of tools offered, and detailed Sender Reputation Score methodology including category weights and grading scale.
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## Blacklist Lookup and Removal Resources
Direct links to the lookup and removal forms for the most impactful email blacklists:
- **Spamhaus**: https://check.spamhaus.org/ - Look up IP or domain across SBL, XBL, PBL, and DBL. Self-service removal available.
- **Barracuda (BRBL)**: https://www.barracudacentral.org/lookups - Check and request removal from the Barracuda Reputation Block List.
- **SpamCop**: https://www.spamcop.net/bl.shtml - Check your IP on SpamCop. Listings auto-expire in 24-48 hours.
- **SORBS**: Decommissioned in 2024. No longer maintained or processing delisting requests.
- **CBL (Composite Blocking List)**: https://www.abuseat.org/lookup.cgi - Check and request removal with diagnostic information.
- **UCEPROTECT**: https://www.uceprotect.net/en/rblcheck.php - Check IP across UCEPROTECT Level 1, 2, and 3.
- **Mailspike**: https://mailspike.org/iplookup.html - Look up IP reputation on Mailspike.
- **DroneBL**: https://dronebl.org/lookup - Check if your IP is listed for being part of a botnet or compromised host.
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## Site Information
- **URL**: https://senderreputation.org
- **Type**: Free email deliverability tools and educational resource
- **Signup required**: No
- **Privacy**: No user tracking, no data selling, queries use only public DNS data
- **Contact**: support@senderreputation.org