Email deliverability and testing tools
Asked as “email deliverability tool”, and as “inbox placement and email testing platform”, on behalf of a mid-market B2B software company. 58 first choices recorded across the direct, paraphrase, budget and scale prompts, six models each. Added to the September 2026 Edition; its answers are read by the distilled judge (ai-indexes-judge-qwen3-14b), not the claude-opus-5 judge of the earlier categories: how the two compare.
Standing · first-choice share
34%
Contested · Google Postmaster Tools 9%
34GlockApps09Google Postmaster Tools07MailReach50others
34% of first choices, contested.
The standing
Share is the count of first choices across the direct, paraphrase, budget and scale prompts, over all six models, for a mid-market B2B software company. Ordered by share.
ProductFirst-choice shareNegative rateLabelsQuadrantSince September 2026
02Google Postmaster Tools Lab in the set9%0%30accepted challengernewNew since September 2026: not ranked then, 9% now.
Show the three products at 0%, ordered by negative rate
The floor is 12 points of share, measured: how far the models move a leader on their own when the same questions are asked twice with nothing changed. A larger change is movement; a smaller one is noise, and both are shown. How the floor is measured
Bars are the share of first choices, 0 to 100Every product with at least 10 labels here. Every product name links to its product page.
Google Postmaster Tools is made by Google, whose model Gemini 3.1 Pro is in the set. On the four share prompts that model made it the first choice zero times of 4; the other five models zero times of 20. Lab treatment is defined on the method page; the row is marked, not excluded.
Recommended versus criticized
Every product with at least 10 labels here, on both axes. The 30% line names a quadrant, not the verdict above: that one needs more than 40%.
Criticized challengerCriticized default
Negative label rate →
01G02
03
04
05
06M07
08
09
10
11
12Accepted challengerEndorsed leader
0%First-choice share → · lines at 30% share and 25% negative50%
Key
01GlockApps34%
GlockApps34%02Google Postmaster Tools9%
03MailReach7%
MailReach7%04MXToolbox5%
MXToolbox5%05Mail-Tester5%
Mail-Tester5%06Folderly3%
Folderly3%07Microsoft SNDS3%
08Validity Everest3%
Validity Everest3%09Mailtrap2%
Mailtrap2%10Email on Acid0%
Email on Acid0%11Litmus0%
Litmus0%12ZeroBounce0%
ZeroBounce0%What they warned about
A high negative share on a product with few labels is a warning. A low share on a product with many labels is salience, not sentiment.
Mail-Tester25%
5 of 20 labels negative · 5 of 6 models · 2 hard negative
“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
Litmus23%
5 of 22 labels negative · 5 of 6 models
“Litmus, for example, positions spam testing as part of QA and blocklist/authentication checks, not a guarantee.” GPT-5.4 mini, negative prompt
Validity Everest26%
7 of 27 labels negative · 5 of 6 models
“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
ZeroBounce25%
5 of 20 labels negative · 4 of 6 models · 1 hard negative
“ZeroBounce only handles the list side of deliverability, not the content or infrastructure side.” Claude Haiku 4.5, negative prompt
What they cite
Citations exist only for the models that return a source list: fourteen of the six in this edition.
Sites the answers cite
79 of 84 answers in this category came back with a source list, from 14 of 6 models: citations where the model returns them, or the search results it consulted. 1059 links across 201 sites, every framing counted. Ranked by the number of answers carrying the site or page.
vendor site · Mailtrap35 answers · 41 citations · 12 models
vendor site · Saleshandy27 answers · 32 citations · 10 models
27 answers · 29 citations · 12 models
vendor site · Amplemarket27 answers · 27 citations · 11 models
vendor site · Instantly25 answers · 37 citations · 10 models
vendor site · Guideflow24 answers · 29 citations · 11 models
vendor site · Sender23 answers · 29 citations · 9 models
vendor site · MailReach21 answers · 34 citations · 12 models
vendor site · Prospeo20 answers · 23 citations · 10 models
20 answers · 20 citations · 11 models
19 answers · 21 citations · 11 models
vendor site · Brevo19 answers · 19 citations · 8 models
Pages the answers cite
The ten pages named in the most answers, by full address. A page here is one the models returned with a recommendation, not one the index endorses.
26 answers · 11 models
23 answers · 9 models
20 answers · 10 models
20 answers · 11 models
18 answers · 10 models
18 answers · 10 models
18 answers · 9 models
17 answers · 8 models
17 answers · 8 models
17 answers · 7 models
Search against answers
Each company's standing in the answers beside its site's footprint in Google search, one row a site: the products the models named on it with their shares, and the share they add up to; monthly searches on Google, and DataForSEO's estimate of AI search demand (modeled from search signals, directional, not a count of queries to any assistant), for the most-searched of the company's and its products' names (the name is in each row's hover text); estimated monthly organic visits to the site; and its best position in Google's top ten for “best email deliverability tool”, “email deliverability tool”. US estimates from DataForSEO and Google's Ads Transparency Center. A small company's site, or a mid-sized company's site for its flagship, is marked company; a product on a large parent's site (Google, Microsoft) has no site figures. A column with no figures for this category is left out, and an empty cell means none were seen, not none exist. Two measurements side by side: neither is read as the cause of the other.
| Company and products | Share | Own site cited | Name searches, Google | AI search demand, est. | Organic visits | Paid search a month, est. | Google ads, last 30 days | Best Google position |
|---|---|---|---|---|---|---|---|---|
| GlockApps glockapps.com | 34% | 148 | 1,600 | 3 | 8,647 | 1 | ||
| Google parent site Google Postmaster Tools 9% | 9% | 77 | 6,600 | 24 | ||||
| MailReach mailreach.co | 7% | 62 | 1,300 | 5 | 12,483 | 112 | ||
| MXToolbox mxtoolbox.com | 5% | 71 | 60,500 | 126 | 453,570 | 18 | ||
| Mail-Tester mailtester.com | 5% | 51 | 5,400 | 93 | 3,496 | 4 | ||
| Validity validity.com Validity Everest 3%, Validity Engage 2% | 5% | 88 | 140 | 0 | 24,467 company | $264 | 120 | |
| Folderly folderly.com | 3% | 52 | 880 | 11 | 2,464 | 8 | ||
| Microsoft parent site Microsoft SNDS 3% | 3% | 41 | 2,240,000 | 403,136 | ||||
| Yahoo yahoo.com Yahoo Sender Hub 3% | 3% | 13 | ||||||
| Mailtrap mailtrap.io | 2% | 56 | 2,900 | 53 | 84,286 | 1 |
Google's top ten for the two searches hold 17 sites; 0 of them are among the sites the models cited here. The first result for “best email deliverability tool” is devopsschool.com.
How they answered
Six framings of the same buying question, each sent to every model in a fresh session with search on. One row per model, so a row shows whether it held its answer under rewording, what it named when cost was the constraint, and what it argued against. Computed from the raw judge labels.ShowHide
How they answered
Six framings of the same buying question, each sent to every model in a fresh session with search on. One row per model, so a row shows whether it held its answer under rewording, what it named when cost was the constraint, and what it argued against. Computed from the raw judge labels.
ShowHideModelDirect“What is the best email deliverability tool for a mid-market B2B company?”Paraphrase“Which inbox placement and email testing platform would you recommend to a mid-sized B2B company?”Comparative“What are the top email deliverability and testing tools and how do they differ?”Budget-constrained“What is the best email deliverability tool for a company with a limited budget?”Scale-constrained“We are a 500 person company evaluating an email deliverability tool. What should we look at?”Negative“Which email deliverability and testing tools should I avoid or be cautious about?”
Claude Opus 5no first choiceno first choiceno first choiceno first choiceno first choicenothing named
Claude Opus 4.8no first choiceno first choiceno first choiceno first choiceno first choicenothing named
GPT-6 Astrano first choiceno first choiceno first choiceno first choiceno first choicenothing named
GPT-5.6 Solno first choiceno first choiceno first choiceno first choiceno first choicenothing named
Gemini 3.1 Prono first choiceno first choiceno first choiceno first choiceno first choicenothing named
Perplexity Sonar Prono first choiceno first choiceno first choiceno first choiceno first choicenothing named
Bold is the first choiceAlternatives are counted; the count opens them.What the answer argued against
The record
One row per call: the version string exactly as returned, whether the model searched, sources cited, and latency. Full answer text is in the free responses file. Download the record
Zero rows: every prompt, every model, every answer.
| Prompt | Model | Version string | Time (UTC) | Searched | Sources | Latency |
|---|
Normalization in this category
Every judgment call made between the raw labels and the numbers above, listed so it is visible and reversible.
ShowHide
Category-scoped readings
Validity read as Validity Everest
Validity (Everest) read as Validity Everest
Validity (InboxReady) read as Validity Everest
Unresolved, counted raw
AboutMyEmail
Email Tool Tester
GetResponse built-in deliverability
GlacierApps
Glock Apps
GlockApps Warm‑up
Hunter Sequences
Instantly Warmup
MailBrace
Mailercloud Email Verifier
Mailforge.ai
OnDMARC
Red Sift
SMTP.com Reputation Defense
SURBL
Salesforce (Einstein)
Spamcheck by Postmark
Spamhaus
URIBL
emailwarmup.com
Discontinued, still offered
No shut-down product was recommended here.