# RelentlessIdentity, free, POST /client/probe: Email verification API

> Use Probe when you already know the exact email address and want a compact deliverability verdict.

RelentlessIdentity's email verification API on its Free plan. It costs $0.00 per 1,000 emails. RelentlessIdentity's docs list 2 of the 6 key fields we check: Address, Deliverability.
We haven't run RelentlessIdentity through [our email verification API benchmark](https://datacircle.dev/best-email-verification-api.txt) yet.
This plan is free. We rank 3,952 plans for email verification APIs by price. Half the plans cost $1.999 per 1,000 emails or less.
[treg's top-up from $10](https://datacircle.dev/validate-email-apis/treg/top-up-from-10/llms.txt) is the cheapest paid plan per 1,000 emails: $0.00 on average. treg asks one provider after another until one answers. You pay $68.365 per 1,000 emails when no provider answers.
[Disify's $9 monthly plan (/email)](https://datacircle.dev/validate-email-apis/disify/9-monthly-starter-post-email/llms.txt) covers any number of emails. Disify's $9 monthly plan costs less up front than treg's top-up from $10.
[pingutil](https://datacircle.dev/validate-email-apis/pingutil/free-api-key-post-v1-verify/llms.txt), [MailTester Ninja](https://datacircle.dev/validate-email-apis/mailtester-ninja/23-99-monthly/llms.txt) and [Giggal](https://datacircle.dev/validate-email-apis/giggal/39-pack-50000-credits-post-v1-verify/llms.txt) are the best email verification API providers in the Datacircle benchmark.

- This page: https://datacircle.dev/validate-email-apis/relentlessidentity/free-post-client-probe
- [Email validation API: 200+ verification providers compared](https://datacircle.dev/best-email-verification-api.txt)
- Get it: https://relentlessidentity.com/pricing?utm_source=datacircle.dev&utm_medium=referral&utm_campaign=email-verification-api-pricing
- Request: `POST https://api.relentlessidentity.com/client/probe`
- API key: with the plan, on https://relentlessidentity.com/pricing?utm_source=datacircle.dev&utm_medium=referral&utm_campaign=email-verification-api-pricing
- Its API docs: https://relentlessidentity.com/docs/rest-api-reference?utm_source=datacircle.dev&utm_medium=referral&utm_campaign=email-verification-api-pricing
- Sold by: RelentlessIdentity (https://relentlessidentity.com?utm_source=datacircle.dev&utm_medium=referral&utm_campaign=email-verification-api-pricing)
- Checked: 2026-11-05

## In the answer

- Completeness: 33%
- Address: ✓
- Deliverability: ✓

## Price

- $ per 1,000 emails: $0.00
- Per: call
- Billing: free

## Aggregators

- Aggregators: none

## Charges

- Also pays for: from the same budget: Find a work email · Schedule a finder batch · Verify many email addresses · Schedule a probe batch

## Not found

- $ per 1,000: $0.00

## Catch-all

- $ per 1,000: $0.00

## In their words

- Their pitch: Use Probe when you already know the exact email address and want a compact deliverability verdict.

## Data

- Freshness: live
- What it checks: mail servers, mailbox
- Keep data: no limit
- Use data: You may use the service only for lawful professional and business purposes, including sales and marketing validation, SaaS data hygiene, recruiting, fraud prevention, underwriting, and account verification. You agree not to: Use the service for spam, scams, or harassment, Discover or disclose consumer personal email addresses, Attempt credential attacks, phishing, or account takeover, Interfere with or disrupt the service, Introduce viruses, malware, or harmful code, Use the service to facilitate illegal activity, Violate the rights of others or evade privacy preferences

## Plan

- Pay: $0

## Rate limit

- Batch: 1

## Speed

- Answer: in the call

## The call

- You send: email
- Method: POST
- Path: /client/probe

## About the plan

- Plan: Free
- Who can get it: anyone 16 or older, for lawful professional and business purposes

## The 10 fields the plan's answer can hold

state, outcome, email address, is alias, alias original, alias resolved, catch-all, identity providers, MX hosts, request ID

## RelentlessIdentity's plans (23)

- [RelentlessIdentity, free, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/free-post-client-probe/llms.txt): $0.00 per 1,000, 33% complete, live
- [RelentlessIdentity, $14 pack, $14 Pay as you go, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/14-pack-14-pay-as-you-go-post-client-probe/llms.txt): $5.602 per 1,000, 33% complete, live
- [RelentlessIdentity, $29 pack, $29 Pay as you go, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/29-pack-29-pay-as-you-go-post-client-probe/llms.txt): $5.489 per 1,000, 33% complete, live
- [RelentlessIdentity, $49 pack, $49 Pay as you go, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/49-pack-49-pay-as-you-go-post-client-probe/llms.txt): $5.378 per 1,000, 33% complete, live
- [RelentlessIdentity, $99 pack, $99 Pay as you go, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/99-pack-99-pay-as-you-go-post-client-probe/llms.txt): $5.272 per 1,000, 33% complete, live
- [RelentlessIdentity, $249 pack, $249 Pay as you go, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/249-pack-249-pay-as-you-go-post-client-probe/llms.txt): $5.166 per 1,000, 33% complete, live
- [RelentlessIdentity, $499 pack, $499 Pay as you go, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/499-pack-499-pay-as-you-go-post-client-probe/llms.txt): $5.063 per 1,000, 33% complete, live
- [RelentlessIdentity, $999 pack, $999 Pay as you go, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/999-pack-999-pay-as-you-go-post-client-probe/llms.txt): $4.961 per 1,000, 33% complete, live
- [RelentlessIdentity, $14 monthly, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/14-monthly-post-client-probe/llms.txt): $3.921 per 1,000, 33% complete, live
- [RelentlessIdentity, $29 monthly, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/29-monthly-post-client-probe/llms.txt): $3.842 per 1,000, 33% complete, live
- [RelentlessIdentity, $49 monthly, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/49-monthly-post-client-probe/llms.txt): $3.766 per 1,000, 33% complete, live
- [RelentlessIdentity, $99 monthly, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/99-monthly-post-client-probe/llms.txt): $3.69 per 1,000, 33% complete, live
- [RelentlessIdentity, $249 monthly, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/249-monthly-post-client-probe/llms.txt): $3.617 per 1,000, 33% complete, live
- [RelentlessIdentity, $499 monthly, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/499-monthly-post-client-probe/llms.txt): $3.545 per 1,000, 33% complete, live
- [RelentlessIdentity, $999 monthly, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/999-monthly-post-client-probe/llms.txt): $3.474 per 1,000, 33% complete, live
- [RelentlessIdentity, $168 yearly, $168 Annual, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/168-yearly-168-annual-post-client-probe/llms.txt): $3.268 per 1,000, 33% complete, live
- [RelentlessIdentity, $348 yearly, $348 Annual, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/348-yearly-348-annual-post-client-probe/llms.txt): $3.202 per 1,000, 33% complete, live
- [RelentlessIdentity, $588 yearly, $588 Annual, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/588-yearly-588-annual-post-client-probe/llms.txt): $3.138 per 1,000, 33% complete, live
- [RelentlessIdentity, $1,188 yearly, $1,188 Annual, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/1188-yearly-1188-annual-post-client-probe/llms.txt): $3.076 per 1,000, 33% complete, live
- [RelentlessIdentity, $2,988 yearly, $2,988 Annual, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/2988-yearly-2988-annual-post-client-probe/llms.txt): $3.014 per 1,000, 33% complete, live
- [RelentlessIdentity, $5,988 yearly, $5,988 Annual, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/5988-yearly-5988-annual-post-client-probe/llms.txt): $2.954 per 1,000, 33% complete, live
- [RelentlessIdentity, $11,988 yearly, $11,988 Annual, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/11988-yearly-11988-annual-post-client-probe/llms.txt): $2.896 per 1,000, 33% complete, live
- [RelentlessIdentity, contact us, Custom plan, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/contact-us-custom-plan-post-client-probe/llms.txt): 33% complete, live

## RelentlessIdentity's calls for this API (3)

- `POST /client/jobs/probe-batch`: [RelentlessIdentity, free, POST /client/jobs/probe-batch](https://datacircle.dev/validate-email-apis/relentlessidentity/free-post-client-jobs-probe-batch/llms.txt)
- `POST /client/probe`: [RelentlessIdentity, free, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/free-post-client-probe/llms.txt)
- `POST /client/probe/batch`: [RelentlessIdentity, free, POST /client/probe/batch](https://datacircle.dev/validate-email-apis/relentlessidentity/free-post-client-probe-batch/llms.txt)

## RelentlessIdentity's APIs (2)

- [RelentlessIdentity: email finder API pricing, 23 plans, POST /client/attempt](https://datacircle.dev/find-email-apis/relentlessidentity/free-post-client-attempt/llms.txt)
- [RelentlessIdentity: email finder API pricing, 23 plans, POST /client/jobs/finder](https://datacircle.dev/find-email-apis/relentlessidentity/free-post-client-jobs-finder/llms.txt)
- [RelentlessIdentity: email verification API pricing, 23 plans, POST /client/probe](https://datacircle.dev/validate-email-apis/relentlessidentity/free-post-client-probe/llms.txt)

## RelentlessIdentity: email verification API alternatives

- [GetProspect, $29 pack, 10,000 verifications, POST /v2/email-verifications](https://datacircle.dev/validate-email-apis/getprospect/29-pack-10000-verifications-post-v2-email-verifications/llms.txt): $2.90 per 1,000, 50% complete, live
- [Bounceless, $29 pack, 10,000 credit pack, POST /v1/requests, Create a batch (emails)](https://datacircle.dev/validate-email-apis/bounceless/29-pack-10000-credit-pack-post-v1-requests-10000-credits/llms.txt): $2.90 per 1,000, 50% complete, live
- [WhoisXML API, $1,740 yearly, Yearly subscription 50,000 Queries, GET /api/v3](https://datacircle.dev/validate-email-apis/whoisxml-api/1740-yearly-yearly-subscription-50000-queries-get-api-v3/llms.txt): $2.90 per 1,000, 50% complete, live
- [MailTester, $29 pack](https://datacircle.dev/validate-email-apis/mailtester/29-pack/llms.txt): $2.90 per 1,000, 50% complete, live

## Sources

From each provider's own pricing page and docs, and from what providers tell us. We read this row from these pages on 2026-11-05.

- https://relentlessidentity.com/?utm_source=datacircle.dev&utm_medium=referral&utm_campaign=email-verification-api-pricing
- https://relentlessidentity.com/acceptable-use?utm_source=datacircle.dev&utm_medium=referral&utm_campaign=email-verification-api-pricing
- https://relentlessidentity.com/api/reference/spec?utm_source=datacircle.dev&utm_medium=referral&utm_campaign=email-verification-api-pricing
- https://relentlessidentity.com/docs/catch-all-verification?utm_source=datacircle.dev&utm_medium=referral&utm_campaign=email-verification-api-pricing
- https://relentlessidentity.com/docs/crypto-payments?utm_source=datacircle.dev&utm_medium=referral&utm_campaign=email-verification-api-pricing
- https://relentlessidentity.com/docs/response-semantics?utm_source=datacircle.dev&utm_medium=referral&utm_campaign=email-verification-api-pricing
- https://relentlessidentity.com/docs/rest-api-reference?utm_source=datacircle.dev&utm_medium=referral&utm_campaign=email-verification-api-pricing
- https://relentlessidentity.com/llms.txt?utm_source=datacircle.dev&utm_medium=referral&utm_campaign=email-verification-api-pricing
- https://relentlessidentity.com/pricing?utm_source=datacircle.dev&utm_medium=referral&utm_campaign=email-verification-api-pricing
- https://relentlessidentity.com/privacy?utm_source=datacircle.dev&utm_medium=referral&utm_campaign=email-verification-api-pricing
- https://relentlessidentity.com/terms?utm_source=datacircle.dev&utm_medium=referral&utm_campaign=email-verification-api-pricing