List your tool
Free

mailX

Free email deliverability checker that diagnoses SPF, DKIM, DMARC, and blacklist issues in one report.

3.8 AI Infrastructure & Agent Tooling
3.8 Good 3.8
Free with no signup barrier for a fast deliverability check Narrow single-purpose scope rather than a full email marketing or sending platform
Reviewed by Challenging Voice Editorial · Updated Jul 2026 How we rate
PricingFree
Free planYes
CompanyMailwarm
PlatformsAPI, Web
CategoryAI Infrastructure & Agent Tooling
Founded2020
Last reviewedJul 2026

Is this your tool?

  • Claim this listing. Sign in with an email at themailx.com to manage it. Claim mailX
  • Get into the top 5 of AI Infrastructure & Agent Tooling. 5 of 5 spots open, from $159/month. See positions
  • Something out of date? Owners can request edits from My listings; anyone can tell us.
Ask AI about mailX ChatGPT Claude Perplexity

Overview

mailX is a free email deliverability diagnostic tool that checks SPF, DKIM, DMARC, MX records, and blacklist status in one report and explains why messages land in spam. It is built by Mailwarm, a Y Combinator S20 company founded in 2020 that has focused on email deliverability since its start, with mailX launched as a newer, more specialized product from that team in 2026.

The tool runs a full deliverability check from the browser with no signup or API key required, so a marketer or developer can get a report in seconds. Beyond the web interface, mailX exposes a JSON API and an MCP server so AI agents can query deliverability data directly, positioning the product for both human and agentic use alongside Mailwarm's original inbox-warming service.

mailX fits developers, marketers, and increasingly AI agents troubleshooting why outbound email fails to reach the inbox. The diagnostic tool itself carries no price and requires no account; the company's revenue instead comes from Mailwarm's separate email warmup product.

Key features

  • One-click SPF, DKIM, DMARC, MX, and blacklist checks
  • Consolidated deliverability report explaining spam placement causes
  • No signup or API key required for web use
  • JSON API for programmatic access
  • MCP server for direct use by AI agents
  • Built by the team behind Mailwarm's inbox-warming product

Screenshots & demo

Demo video

Screenshots

mailX screenshot 1

Pricing

mailX offers a free plan, with paid upgrades for higher limits and more features.

  • Pricing modelFree
  • Starting priceFree
  • Free planYes
Visit mailX

Pricing is provided as a guide. Check the official site for the latest plans.

Is mailX expensive?

mailX has no advertised paid tier. Among the 75 priced tools we list in AI Infrastructure & Agent Tooling, the median entry price is $29 a month.

55% of AI Infrastructure & Agent Tooling tools in the directory offer a free tier, and this is one of them.

Compared against every priced listing in AI Infrastructure & Agent Tooling, recalculated as the catalogue changes. Method and the full market breakdown are in our AI tool pricing study.

Pros & cons

Pros

  • Free with no signup barrier for a fast deliverability check
  • MCP server access is a differentiator most deliverability checkers lack
  • Backed by a Y Combinator company with deliverability-specific focus since 2020
  • Consolidates several separate DNS and authentication checks into one report

Cons

  • Narrow single-purpose scope rather than a full email marketing or sending platform
  • No paid tier means no dedicated support commitment for the tool itself
  • Deeper deliverability fixes still require action outside the tool, such as DNS changes or IP warmup
  • Newer product with a shorter track record than established checkers like MxToolbox

How it compares

ToolRatingFreeFromBest known for
mailX (this tool)3.8YesFreeOne-click SPF, DKIM, DMARC, MX, and blacklist checks
Datumbox3.0YesFreeREST API for sentiment analysis and topic classification
SendHQ3.6No$9/moDeveloper API for sending and receiving transactional email
Bird4.0No—One API for email, SMS, WhatsApp, Apple Messages and voice

Alternatives to mailX

4 tools matched to mailX on what they do, their category and their price.

Compare all mailX alternatives →

Head to head: mailX vs Datumbox · mailX vs SendHQ · mailX vs Bird · mailX vs KlavisAI

Frequently asked questions

What is mailX?
mailX is a free email deliverability diagnostic tool that checks SPF, DKIM, DMARC, MX records, and blacklist status in one report and explains why messages land in spam.
Is mailX free?
Yes, mailX offers a free plan. Paid plans unlock more features and higher usage limits.
What are the best mailX alternatives?
The closest matches in the directory are Datumbox, SendHQ, and Bird, compared side by side above.

Reviews

3.8 Editorial rating No reviews yet

Write a review

More tools like mailX

Sinch

4.1

Communications platform with messaging, voice, email and verification APIs, plus AI features: artificial traffic detection, Smart Conversations with sentiment detection and PII masking, Voice Relay for AI phone calls and an MCP server.

Contact for Pricing AI Infrastructure & Agent Tooling
View details Visit