# MXToolbox vs Mail-Tester: which do AI models recommend for email deliverability, October 2026

GTM AI Recommendation Index, October 2026 Edition, Email deliverability and testing tools. Zero of fourteen models named MXToolbox first on the direct prompt; zero named Mail-Tester. Page: https://gtm-ai-index.com/marketing/email-deliverability-and-testing/mxtoolbox-vs-mail-tester/

| | First-choice share | Rank | Negative rate | Labels | Models naming it |
|---|---|---|---|---|---|
| MXToolbox | 5% | #4 of 12 | 10% | 31 | 12 of 14 |
| Mail-Tester | 5% | #5 of 12 | 25% | 20 | 11 of 14 |

## The direct prompt, model by model

- DeepSeek V4 Flash: neither first, one named (first choices: MailReach) (alternatives: GlockApps, Google Postmaster Tools, MXToolbox)
- MiniMax M2.5: neither first, one named (first choices: Folderly, Mailtrap) (alternatives: EasyDMARC, MXToolbox)
- Claude Haiku 4.5: neither named (first choices: InboxArmy, MailBrace) (alternatives: Folderly, GlockApps, HubSpot, Mailsoftly)
- GPT-5.4 mini: neither named (first choices: Mailgun Optimize) (alternatives: GlockApps)
- Gemini 3.5 Flash: neither named (first choices: Allegrow, GlockApps) (alternatives: Mailgun Optimize, ZeroBounce)
- Perplexity Sonar: neither named (first choices: GlockApps) (alternatives: Amplemarket, MailReach, NeverBounce)
- Grok 4.1 Fast: neither named (first choices: GlockApps) (alternatives: MailReach, Validity Everest, Warmy.io)
- Mistral Small: neither named (first choices: Folderly, GlockApps) (alternatives: MailReach, Zoho CRM)
- Llama 4 Maverick: neither named (first choices: GlockApps)
- Qwen 3.7 Flash: neither named (first choices: GlockApps) (alternatives: 250ok, Instantly, Kickbox, Lemlist, Valimail, ZeroBounce)
- Kimi K2: neither named (first choices: GlockApps, Instantly) (alternatives: HubSpot Sales Hub, MailReach)
- GLM 4.7 FlashX: neither named (first choices: GlockApps, MailReach) (alternatives: Folderly, Warmy)
- GPT-6 Luna: neither named (first choices: Validity Everest) (alternatives: GlockApps)
- Muse Glimmer 30B: neither named (first choices: GlockApps) (alternatives: MailReach, Validity Everest)

## What the models said about MXToolbox

- "MxToolbox is an infrastructure diagnostic tool, not a campaign email testing tool... best used only for specific DNS and infrastructure checks, not comprehensive campaign testing." (Claude Haiku 4.5, negative prompt, hard negative)
- "Free tools like Mail Tester and MxToolbox handle basic checks but lack the depth for production workflows." (Muse Glimmer 30B, negative prompt, soft negative)
- "lack depth for production-scale testing, inbox placement simulation, or ongoing monitoring" (Grok 4.1 Fast, negative prompt, soft negative)
- "Best free option: Stack Google Postmaster Tools, Microsoft SNDS, Yahoo Sender Hub, MXToolbox, Mail Tester, AboutMyEmail, and Sender Hub." (GLM 4.7 FlashX, budget prompt, first choice)
- "free monitoring stack with Google Postmaster Tools, Microsoft SNDS, MXToolbox, and Yahoo Sender Hub" (Perplexity Sonar, budget prompt, first choice)
- "Start with free tools → Google Postmaster Tools + MXToolbox + Mail-Tester free tier" (Kimi K2, budget prompt, first choice)

## What the models said about Mail-Tester

- "Mail-Tester scores against a single seed address, so it can't tell you where your email lands across a multi-ISP seed network" (Claude Haiku 4.5, negative prompt, hard negative)
- "These are inaccurate and misleading... do not base business decisions on them." (DeepSeek V4 Flash, negative prompt, hard negative)
- "Avoid: Relying solely on these web-based scores. They are useful for a quick syntax check but should not be your primary deliverability testing tool." (GLM 4.7 FlashX, negative prompt, soft negative)
- "Mail-Tester for occasional pre-send checks of a message and its sending setup. It allows up to 3 free tests per day." (GPT-6 Luna, budget prompt, first choice)
- "The best email deliverability tool for a company with a limited budget is Mail-Tester or Unspam for pre-send testing" (Llama 4 Maverick, budget prompt, first choice)
- "Start with free tools → Google Postmaster Tools + MXToolbox + Mail-Tester free tier" (Kimi K2, budget prompt, first choice)

Share is the count of first choices across the direct, paraphrase, budget and scale prompts over all fourteen models, for a mid-market B2B company; rank is within the category. Comparisons are drawn for the top eight products in each category. Published under CC BY 4.0; the output is the models' output, and nothing here is a recommendation by the index.