Free

mailX

Name: mailX
Author: Challenging Voice

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

3.8 Good 3.8

Bottom line: mailX is a capable ai infrastructure & agent tooling tool, best known for one-click SPF, DKIM, DMARC, MX, and blacklist checks. It has a free plan.

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

Best forAI Infrastructure & Agent Tooling

Founded2020

Last reviewedJul 2026

UpdatedJul 2026

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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

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.

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

Tool	Rating	Free	From	Best known for
mailX (this tool)	3.8	Yes	Free	One-click SPF, DKIM, DMARC, MX, and blacklist checks
Lambda	4.1	No	—	On-demand and reserved NVIDIA GPU cloud instances with published hourly rates
Tavily	4.1	Yes	Free	Search API returning clean, structured results optimized for LLM consumption
CoreWeave	4.3	No	—	Large-scale NVIDIA GPU clusters purpose-built for AI training and inference

Our verdict

3.8 / 5 3.8

mailX is a solid ai infrastructure & agent tooling tool, best known for one-click SPF, DKIM, DMARC, MX, and blacklist checks. It offers a free plan.

What makes it different: mailX stands out for one-click SPF, DKIM, DMARC, MX, and blacklist checks.

How we score it

Overall 3.8

Value for money 4.7

Feature depth 4.9

Popularity 3.7

Best for ProfessionalsTeamsCreatorsCurious learners

Frequently asked questions

What is mailX?

mailX is an ai infrastructure & agent tooling tool listed in the Challenging Voice directory. Free email deliverability checker that diagnoses SPF, DKIM, DMARC, and blacklist issues in one report.

Is mailX free?

Yes, mailX offers a free plan. Paid plans unlock more features and higher usage limits.

What are the best mailX alternatives?

Popular alternatives to mailX include Hailo, Nexa SDK, and AgentOps. Browse them all in the AI Infrastructure & Agent Tooling category.

Is mailX any good?

mailX scores 3.8 out of 5 based on our editorial review.