Free tools
Free email deliverability and SMTP diagnostic tools
25 free browser tools for email authentication, DNS, SMTP connectivity, reputation, and message analysis — plus integrated diagnostics in MailFleet desktop for Windows, macOS, and Linux.
At a glance
- What it is
- A free hub of 25 email deliverability and SMTP diagnostic tools published by MailFleet.
- Who it is for
- Email operators, agencies, SaaS teams, deliverability consultants, and technical marketers preparing permission-based campaigns.
- Main capabilities
- SPF, DKIM, DMARC, BIMI, MTA-STS, TLS-RPT, MX/TXT/CNAME/DNS lookups, blacklist checks, SMTP diagnostics, SpamAssassin, domain health, and message analysis.
- Platforms
- Browser-based tools at mailfleet.app/tools; integrated checks in MailFleet desktop for Windows, macOS, and Linux.
- Responsible use
- Diagnostic preparation for permission-based email only — not spam, list harvesting, or filter evasion.
What are MailFleet email deliverability tools?
Free DNS, authentication, SMTP, and content checks before you send permission-based campaigns.
The MailFleet tools hub is a free collection of email DNS, authentication, SMTP, reputation, and content diagnostic utilities. Operators use these checks to validate sending domains, troubleshoot provider configuration, and prepare permission-based campaigns before launch.
Each tool page explains what the check does, why it matters for deliverability, common issues, and how MailFleet desktop software extends the same workflow with integrated pre-send diagnostics, campaign logs, and provider profiles.
Browser tools are diagnostic previews — they help you prepare workflows and understand signals receivers evaluate. MailFleet desktop connects to your SMTP and API providers for full campaign control with SpamAssassin checks, capacity scoring, webhooks, and exportable reports.
Browse by category
Jump to authentication, DNS, SMTP, reputation, or content tools — each group maps to a common pre-send checklist.
Complete tool index (25 tools)
Every free MailFleet diagnostic with icons, categories, and direct links — filter by topic or search for audits, onboarding, and pre-send checklists.
- 01Reputation & health
Email Blacklist Checker
Check if your domain or IP appears on major email blacklists. Understand reputation risk before launching campaigns with MailFleet.
Open tool - 02SMTP & connectivity
SMTP Diagnostics
Free SMTP diagnostics tool: test host connectivity, STARTTLS/SSL, AUTH login, and send HTML or plain test messages with verbose protocol logs.
Open tool - 03Content & message analysis
SpamAssassin Checker
Free SpamAssassin checker: analyze subject and HTML/plain body for spam score, triggered rules, and fix recommendations before sending campaigns.
Open tool - 04Email authentication
SPF Checker
Validate SPF DNS records, authorized senders, lookup count, and syntax for your sending domain before configuring providers in MailFleet.
Open tool - 05Email authentication
DKIM Checker
Scan your domain for all common DKIM selectors, validate public keys, explain every DNS tag, and report key strength — no manual selector lookup.
Open tool - 06Email authentication
DMARC Checker
Check DMARC DNS records, policy mode, aggregate reporting addresses, and alignment guidance for your organizational sending domain.
Open tool - 07DNS lookups
MX Lookup
Look up MX records, priority values, and mail hostnames for any domain to understand inbound mail routing and DNS configuration.
Open tool - 08Content & message analysis
Email Header Analyzer
Parse raw email headers to review SPF, DKIM, and DMARC authentication results, routing hops, delays, and delivery troubleshooting signals.
Open tool - 09DNS lookups
Reverse DNS Checker
Verify PTR reverse DNS records for sending IP addresses and check forward-confirmed reverse DNS alignment with your SMTP hostname.
Open tool - 10SMTP & connectivity
SMTP Port Checker
Test whether common SMTP ports 25, 465, and 587 respond on a mail host from your network before configuring MailFleet provider profiles.
Open tool - 11Reputation & health
Domain Email Health Check
Run a combined email health scan: MX, SPF, DKIM, DMARC, reverse DNS signals, and blacklist status for one domain.
Open tool - 12Content & message analysis
Email Subject Line Tester
Review subject line length, mobile preview truncation, and common spam trigger words before sending.
Open tool - 13Content & message analysis
HTML Email Preview
Preview HTML email markup in a sandboxed browser frame before importing templates into MailFleet. Catch layout, image, and link issues early.
Open tool - 14Content & message analysis
Unsubscribe Link Checker
Verify unsubscribe links are present, use HTTPS, and follow List-Unsubscribe header best practices for permission-based marketing compliance.
Open tool - 15Content & message analysis
Bounce Code Lookup
Look up SMTP reply codes and delivery status notification bounce reasons from campaign logs. Map errors to fixes and list hygiene actions.
Open tool - 16Email authentication
BIMI Checker
Check BIMI DNS records, logo location, VMC requirements, and selector configuration for branded inbox display on supporting mailbox providers.
Open tool - 17Email authentication
MTA-STS Checker
Validate MTA-STS DNS records and policy files that require TLS for inbound mail to your domain, reducing downgrade and interception risk.
Open tool - 18Email authentication
TLS-RPT Checker
Look up TLS-RPT DNS records and reporting addresses that collect aggregate TLS failure reports for MTA-STS and DANE troubleshooting.
Open tool - 19DNS lookups
TXT Record Lookup
Look up all TXT DNS records for a domain. SPF, DKIM, DMARC, BIMI, and verification tokens often live in TXT records.
Open tool - 20DNS lookups
CNAME Lookup
Resolve CNAME records for mail-related hostnames such as tracking domains, DKIM CNAME delegations, and provider aliases.
Open tool - 21DNS lookups
DNS A Record Lookup
Look up DNS A records (IPv4) for mail hostnames, SMTP servers, and MX targets to verify resolution and routing.
Open tool - 22DNS lookups
DNS AAAA Record Lookup
Look up DNS AAAA records (IPv6) for mail hostnames and MX targets. IPv6 is increasingly used for SMTP and inbound delivery.
Open tool - 23DNS lookups
SOA Record Lookup
Look up the SOA record for a domain to review primary nameserver, responsible party, serial, and zone timing values.
Open tool - 24DNS lookups
WHOIS Lookup
Review WHOIS registration data for a sending domain: registrar, creation date, expiry, and nameservers for operational due diligence.
Open tool - 25SMTP & connectivity
Open Relay Checker
Test whether an SMTP server improperly relays mail from unauthorized senders. Open relays are abused for spam and get blacklisted quickly.
Open tool
Showing 25 of 25 tools
Email authentication
Email authentication
Email authentication tools validate SPF, DKIM, DMARC, BIMI, MTA-STS, and TLS-RPT records — the DNS signals mailbox providers use to verify sender identity and transport security.
6 tools in this group
- Email authentication
SPF Checker
Validate SPF DNS records, authorized senders, lookup count, and syntax for your sending domain before configuring providers in MailFleet.
Open tool - Email authentication
DKIM Checker
Scan your domain for all common DKIM selectors, validate public keys, explain every DNS tag, and report key strength — no manual selector lookup.
Open tool - Email authentication
DMARC Checker
Check DMARC DNS records, policy mode, aggregate reporting addresses, and alignment guidance for your organizational sending domain.
Open tool - Email authentication
BIMI Checker
Check BIMI DNS records, logo location, VMC requirements, and selector configuration for branded inbox display on supporting mailbox providers.
Open tool - Email authentication
MTA-STS Checker
Validate MTA-STS DNS records and policy files that require TLS for inbound mail to your domain, reducing downgrade and interception risk.
Open tool - Email authentication
TLS-RPT Checker
Look up TLS-RPT DNS records and reporting addresses that collect aggregate TLS failure reports for MTA-STS and DANE troubleshooting.
Open tool
DNS lookups
DNS lookups
DNS lookup tools resolve MX, TXT, CNAME, A, AAAA, SOA, WHOIS, and reverse DNS records for mail hostnames and sending domains.
8 tools in this group
- DNS lookups
MX Lookup
Look up MX records, priority values, and mail hostnames for any domain to understand inbound mail routing and DNS configuration.
Open tool - DNS lookups
Reverse DNS Checker
Verify PTR reverse DNS records for sending IP addresses and check forward-confirmed reverse DNS alignment with your SMTP hostname.
Open tool - DNS lookups
TXT Record Lookup
Look up all TXT DNS records for a domain. SPF, DKIM, DMARC, BIMI, and verification tokens often live in TXT records.
Open tool - DNS lookups
CNAME Lookup
Resolve CNAME records for mail-related hostnames such as tracking domains, DKIM CNAME delegations, and provider aliases.
Open tool - DNS lookups
DNS A Record Lookup
Look up DNS A records (IPv4) for mail hostnames, SMTP servers, and MX targets to verify resolution and routing.
Open tool - DNS lookups
DNS AAAA Record Lookup
Look up DNS AAAA records (IPv6) for mail hostnames and MX targets. IPv6 is increasingly used for SMTP and inbound delivery.
Open tool - DNS lookups
SOA Record Lookup
Look up the SOA record for a domain to review primary nameserver, responsible party, serial, and zone timing values.
Open tool - DNS lookups
WHOIS Lookup
Review WHOIS registration data for a sending domain: registrar, creation date, expiry, and nameservers for operational due diligence.
Open tool
SMTP & connectivity
SMTP & connectivity
SMTP and connectivity tools test server reachability, port availability, TLS negotiation, and open relay risk before you configure providers in MailFleet.
3 tools in this group
- SMTP & connectivity
SMTP Diagnostics
Free SMTP diagnostics tool: test host connectivity, STARTTLS/SSL, AUTH login, and send HTML or plain test messages with verbose protocol logs.
Open tool - SMTP & connectivity
SMTP Port Checker
Test whether common SMTP ports 25, 465, and 587 respond on a mail host from your network before configuring MailFleet provider profiles.
Open tool - SMTP & connectivity
Open Relay Checker
Test whether an SMTP server improperly relays mail from unauthorized senders. Open relays are abused for spam and get blacklisted quickly.
Open tool
Reputation & health
Reputation & health
Reputation and health tools surface blacklist listings and combined domain readiness scores so teams fix DNS and abuse issues before scaling volume.
2 tools in this group
- Reputation & health
Email Blacklist Checker
Check if your domain or IP appears on major email blacklists. Understand reputation risk before launching campaigns with MailFleet.
Open tool - Reputation & health
Domain Email Health Check
Run a combined email health scan: MX, SPF, DKIM, DMARC, reverse DNS signals, and blacklist status for one domain.
Open tool
Content & message analysis
Content & message analysis
Content and message analysis tools review SpamAssassin triggers, subject lines, HTML markup, headers, unsubscribe paths, and bounce codes from campaign logs.
6 tools in this group
- Content & message analysis
SpamAssassin Checker
Free SpamAssassin checker: analyze subject and HTML/plain body for spam score, triggered rules, and fix recommendations before sending campaigns.
Open tool - Content & message analysis
Email Header Analyzer
Parse raw email headers to review SPF, DKIM, and DMARC authentication results, routing hops, delays, and delivery troubleshooting signals.
Open tool - Content & message analysis
Email Subject Line Tester
Review subject line length, mobile preview truncation, and common spam trigger words before sending.
Open tool - Content & message analysis
HTML Email Preview
Preview HTML email markup in a sandboxed browser frame before importing templates into MailFleet. Catch layout, image, and link issues early.
Open tool - Content & message analysis
Unsubscribe Link Checker
Verify unsubscribe links are present, use HTTPS, and follow List-Unsubscribe header best practices for permission-based marketing compliance.
Open tool - Content & message analysis
Bounce Code Lookup
Look up SMTP reply codes and delivery status notification bounce reasons from campaign logs. Map errors to fixes and list hygiene actions.
Open tool
Need integrated checks inside your campaign workflow?
MailFleet desktop runs SpamAssassin checks, capacity scoring, provider tests, webhooks, and exportable logs alongside every campaign — on Windows, macOS, and Linux.
Key takeaways
- MailFleet publishes 25 free email deliverability and SMTP diagnostic tools at mailfleet.app/tools.
- Tools cover authentication (SPF, DKIM, DMARC, BIMI, MTA-STS, TLS-RPT), DNS lookups, SMTP connectivity, reputation, and message analysis.
- Each tool includes FAQs, troubleshooting guidance, and links to MailFleet desktop features and documentation.
- Browser diagnostics complement integrated pre-send checks inside MailFleet for Windows, macOS, and Linux.
- Tools support permission-based email preparation — not spam, harvesting, or filter evasion.
Summary
MailFleet's free tools hub helps email operators validate DNS authentication, inspect SMTP infrastructure, review reputation signals, and analyze message content before permission-based campaigns. For full campaign control with provider profiles, SpamAssassin checks, webhooks, and local logs, use MailFleet desktop email campaign software on Windows, macOS, or Linux.
FAQ
Frequently asked questions about MailFleet tools
Common questions from operators using free email DNS and SMTP diagnostics.
Frequently asked questions
Yes. All tools on the MailFleet tools hub are free to use in the browser for DNS, SMTP, authentication, reputation, and content diagnostics. Integrated production checks are included in MailFleet desktop software.
For regulatory context on commercial email in the United States, see the FTC CAN-SPAM compliance guide.
Delivery note: MailFleet helps users manage campaigns through their own sending providers. Delivery outcomes depend on sender reputation, DNS authentication, content quality, recipient engagement, list quality, provider rules, and mailbox filtering systems.
Get started
Run diagnostics in the browser. Control campaigns on the desktop.
Use free MailFleet tools for pre-send checks, then download MailFleet for full SMTP/API provider management, logs, and reports.
Available on
- Windows 10+
- macOS 12+
- Linux (DEB & RPM)
Same desktop experience across every platform — one workflow for your entire team.