# Mail-Tester vs Validity Everest: 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 Mail-Tester first on the direct prompt; one named Validity Everest. Page: https://gtm-ai-index.com/marketing/email-deliverability-and-testing/mail-tester-vs-validity-everest/

| | First-choice share | Rank | Negative rate | Labels | Models naming it |
|---|---|---|---|---|---|
| Mail-Tester | 5% | #5 of 12 | 25% | 20 | 11 of 14 |
| Validity Everest | 3% | #8 of 12 | 26% | 27 | 12 of 14 |

## The direct prompt, model by model

- GPT-6 Luna: validity everest first (first choices: Validity Everest) (alternatives: GlockApps)
- Grok 4.1 Fast: neither first, one named (first choices: GlockApps) (alternatives: MailReach, Validity Everest, Warmy.io)
- Muse Glimmer 30B: neither first, one named (first choices: GlockApps) (alternatives: MailReach, Validity Everest)
- 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)
- Mistral Small: neither named (first choices: Folderly, GlockApps) (alternatives: MailReach, Zoho CRM)
- DeepSeek V4 Flash: neither named (first choices: MailReach) (alternatives: GlockApps, Google Postmaster Tools, MXToolbox)
- 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)
- MiniMax M2.5: neither named (first choices: Folderly, Mailtrap) (alternatives: EasyDMARC, MXToolbox)

## 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)

## What the models said about Validity Everest

- "its pricing often starts at $20,000 to $65,000/year, making it massive overkill and too expensive for most mid-sized operations" (Gemini 3.5 Flash, paraphrase prompt, soft negative)
- "enterprise suites like *Validity Everest* (which can cost upward of $15,000/year) to be too complex and cost-prohibitive" (Gemini 3.5 Flash, direct prompt, soft negative)
- "The gold standard for enterprise, but likely overkill for mid-sized companies on both features and budget." (DeepSeek V4 Flash, paraphrase prompt, soft negative)
- "The gold standard for larger mid-market and enterprise brands. Extremely deep seed-testing network and comprehensive reputation monitoring, though highly priced." (Gemini 3.5 Flash, scale prompt, first choice)
- "My default pick: Validity Everest" (GPT-6 Luna, direct prompt, first choice)
- "Everest is the largest and most robust platform in the space... generally cost-prohibitive for SMBs." (Gemini 3.5 Flash, comparative prompt, alternative)

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.