# Email deliverability and testing tools for enterprise buyers: what AI models recommend, November 2026

Gane Index, November 2026 Edition. Asked as "email deliverability tool" and as "inbox placement and email testing platform", six framings each, to fourteen models with search on, on behalf of an enterprise B2B company. Added to the November 2026 Edition. Page: https://www.gane.ai/index/gtm/marketing/email-deliverability-and-testing/2026-11/enterprise

**Standing:** Validity Everest leads with 46% of first choices; verdict clear leader. 50 first choices across the direct, paraphrase, budget and scale prompts.

## First-choice share

| Rank | Product | Share | Negative rate | Labels |
|---|---|---|---|---|
| 1 | [Validity Everest](https://www.gane.ai/index/gtm/vendors/validity-everest/index.md) | 46% | 0% | 43 |
| 2 | [Validity Engage](https://www.gane.ai/index/gtm/vendors/validity-engage/index.md) | 10% | 0% | 12 |
| 3 | [GlockApps](https://www.gane.ai/index/gtm/vendors/glockapps/index.md) | 8% | 16% | 50 |
| 4 | [Mailgun Optimize](https://www.gane.ai/index/gtm/vendors/mailgun-optimize/index.md) | 6% | 8% | 13 |
| 5 | [Mailgun](https://www.gane.ai/index/gtm/vendors/mailgun/index.md) | 4% | 5% | 21 |
| 6 | [Inbox Monster](https://www.gane.ai/index/gtm/vendors/inbox-monster/index.md) | 4% | 8% | 13 |
| 7 | [Instantly](https://www.gane.ai/index/gtm/vendors/instantly/index.md) | 4% | 30% | 10 |
| 8 | [Litmus](https://www.gane.ai/index/gtm/vendors/litmus/index.md) | 2% | 16% | 25 |
| 9 | [ZeroBounce](https://www.gane.ai/index/gtm/vendors/zerobounce/index.md) | 2% | 18% | 22 |
| 10 | [SendGrid](https://www.gane.ai/index/gtm/vendors/sendgrid/index.md) | 2% | 14% | 14 |
| 17 | [Microsoft SNDS](https://www.gane.ai/index/gtm/vendors/microsoft-snds/index.md) | 0% | 0% | 14 |
| 18 | [Google Postmaster Tools](https://www.gane.ai/index/gtm/vendors/google-postmaster-tools/index.md) | 0% | 14% | 14 |

Rank is by share of first choices among all 125 products named; products with the same share are tied, and the order among them carries no meaning. The table lists those with at least 10 labels.

## Each model's first choice on the direct prompt

- Claude Haiku 4.5: Salesforce; alternatives HubSpot, Validity Engage, Validity Everest
- GPT-5.4 mini: Validity Engage; alternatives Adobe Marketo Engage, Iterable, Litmus, Salesforce Agentforce Marketing
- Gemini 3.5 Flash: Validity Everest; alternatives Allegrow, BriteVerify, Folderly, GlockApps
- Perplexity Sonar: Validity Engage; alternatives BriteVerify, EasyDMARC, GlockApps, Kickbox
- Grok 4.20: Validity Everest; alternatives Allegrow, GlockApps, Google Postmaster Tools, Microsoft SNDS
- Mistral Small: GlockApps, Validity Engage; alternatives Everest, Mailgun, PowerDMARC
- DeepSeek V4 Flash: Validity Everest; alternatives GlockApps
- Llama 4 Maverick: Validity Everest; alternatives GlockApps, Mailtrap Email Sandbox, ZeroBounce
- Qwen 3.7 Flash: Validity Everest; alternatives Folderly, GlockApps
- Kimi K2: Validity Everest; alternatives Inbox Monster, SendGrid
- GLM 4.7 FlashX: Validity Everest; alternatives GlockApps, Mailgun, SendGrid
- MiniMax M2.5: Amplemarket; alternatives GlockApps, Mailgun, Mailwarm, ZeroBounce
- GPT-6 Luna: Validity's Everest deliverability platform; alternatives Inbox Monster
- Muse Glimmer 30B: Validity Everest; alternatives Amplemarket, GlockApps

## Sources the answers cite

75 of 84 answers came back with a source list, from 14 of 14 models. Sites named in the most answers:

- salesdorado.com: 26 answers, 28 citations
- instantly.ai: 25 answers, 35 citations
- mailgun.com: 23 answers, 46 citations
- validity.com: 20 answers, 30 citations
- g2.com: 20 answers, 28 citations
- amplemarket.com: 19 answers, 19 citations
- unspam.email: 18 answers, 21 citations
- smartlead.ai: 18 answers, 19 citations

Pages named in the most answers:

- https://amplemarket.com/blog/best-email-deliverability-tools (19 answers)
- https://salesdorado.com/en/inbound-marketing/email-testing-tools (19 answers)
- https://smartlead.ai/blog/email-deliverability-services (16 answers)
- https://omnisend.com/blog/email-deliverability-tools (13 answers)
- https://myemailverifier.com/blog/email-deliverability-tools (12 answers)
- https://sender.net/blog/email-deliverability-tools (12 answers)
- https://validity.com/wp-content/uploads/2021/06/Everest-Features.pdf (12 answers)
- https://saleshandy.com/blog/email-deliverability-tools (11 answers)
- https://g2.com/categories/email-deliverability/enterprise (10 answers)
- https://inboxarmy.com/blog/12-best-email-deliverability-tools (9 answers)

## Warned against

- Mail-Tester: 6 of 9 labels negative. "Free consumer-grade checkers such as mail-tester.com for production go/no-go decisions... repeatedly flagged for enterprise use because it scores against a single seed address." (Muse Glimmer 30B, negative prompt)
- GlockApps: 8 of 50 labels negative. "What to Avoid for Your Use Case ... GlockApps | Great for mid-market diagnostics, but priced per test ... scales poorly for enterprise teams." (DeepSeek V4 Flash, budget prompt)
- MailReach: 7 of 13 labels negative. "Traditional Email Warmup Tools (e.g., Warmbox, Mailreach, or generic "inbox warmup" services)... Why avoid/cautious?" (Grok 4.20, negative prompt)
- Folderly: 4 of 16 labels negative. "Tools to be cautious about: Warmup Inbox, Folderly's auto-warm features" (DeepSeek V4 Flash, negative prompt)

## Movement since October 2026

Floor: 11 points of share, measured on the calibration repeat.
Same leader: Validity Everest at 46%.

- GlockApps: 2% to 8%, +6. Inside the floor by 5 points · rank 9 → 3 of 125.
- Mailgun Optimize: 0% to 6%, +6. Inside the floor by 5 points · rank 23 → 4 of 125.
- Validity Engage: 6% to 10%, +4. Inside the floor by 7 points · rank 6 → 2 of 125.
- Litmus: 6% to 2%, −4. Inside the floor by 7 points · rank 2 → 8 of 125.
- SendGrid: 6% to 2%, −4. Inside the floor by 7 points · rank 5 → 10 of 125.
- Mailgun: 6% to 4%, −2. Inside the floor by 9 points · rank 3 → 5 of 125.
- Inbox Monster: 2% to 4%, +2. Inside the floor by 9 points · rank 11 → 6 of 125.
- Instantly: 6% to 4%, −2. Inside the floor by 9 points · rank 7 of 125, unchanged.
- ZeroBounce: 0% to 2%, +2. Inside the floor by 9 points · rank 17 → 9 of 125.
- Folderly: 2% to 0%, −2. Inside the floor by 9 points · rank 10 → 20 of 125.
- MailReach: 2% to 0%, −2. Inside the floor by 9 points · rank 13 → 124 of 125.
- Validity Everest: 45% to 46%, +1. Inside the floor by 10 points · rank 1 of 125, unchanged.

## Record

- Method: https://www.gane.ai/index/gtm/methodology
- License: CC BY 4.0. Cite as Gane Index, November 2026 Edition, www.gane.ai/index/gtm.