> ## Documentation Index > Fetch the complete documentation index at: https://retention.mintlify.site/llms.txt > Use this file to discover all available pages before exploring further. # Email Activity Check > See when an email was last active online. Send one email address per request, or an array of up to 1,000 addresses in a single request. Batch endpoint: provide `emails` (an array of up to 1,000 plaintext addresses) or a single `email`. Duplicate addresses count once (matching is case-insensitive and ignores surrounding whitespace). The response lists only the addresses with known activity, each with its `last_active` date; addresses with no match are omitted from `results`. **Billing:** 1 credit per matched email. Misses are free. Matches are billed in input order until the account's credit balance runs out; any further matches are dropped from the response and `credits_exhausted` is returned as `true`. `match_count` and `credits_charged` both reflect the number of matches actually returned and billed. ## OpenAPI ````yaml POST /api/v1/email_to_activity openapi: 3.0.1 info: title: Retention API version: v1 description: Retention.com identity & data resolution APIs. servers: - url: https://api.rb2b.com security: [] tags: - name: Identity description: >- Core Identity. Resolve a hashed email (or batch) into a shaped person profile. paths: /api/v1/email_to_activity: post: tags: - Email summary: Email Activity Check description: >- See when an email was last active online. Send one email address per request, or an array of up to 1,000 addresses in a single request. Batch endpoint: provide `emails` (an array of up to 1,000 plaintext addresses) or a single `email`. Duplicate addresses count once (matching is case-insensitive and ignores surrounding whitespace). The response lists only the addresses with known activity, each with its `last_active` date; addresses with no match are omitted from `results`. **Billing:** 1 credit per matched email. Misses are free. Matches are billed in input order until the account's credit balance runs out; any further matches are dropped from the response and `credits_exhausted` is returned as `true`. `match_count` and `credits_charged` both reflect the number of matches actually returned and billed. operationId: emailToActivity parameters: [] requestBody: content: application/json: schema: type: object description: >- Provide `emails` (preferred, up to 1,000 addresses) or a single `email`. When both are present, `emails` wins. properties: emails: type: array maxItems: 1000 items: type: string format: email description: >- Email addresses to check, up to 1,000 per request. Blank entries are ignored; duplicates count once (matching is case-insensitive and ignores surrounding whitespace). example: - alice@example.com - bob@example.com email: type: string format: email description: Single email address (alternative to the `emails` array). example: alice@example.com required: true responses: '200': description: Activity results for matched emails (1 credit per match) content: application/json: schema: type: object required: - results - match_count - credits_charged - credits_exhausted properties: results: type: array description: >- One entry per matched (and billed) email, in input order. Emails with no known activity are omitted. items: type: object required: - email - last_active properties: email: type: string format: email description: The input email address, echoed back as supplied. example: alice@example.com last_active: type: string format: date description: >- Date the email was last seen active online (ISO 8601). example: '2026-05-01' match_count: type: integer description: Number of matched emails returned in `results`. example: 1 credits_charged: type: integer description: >- Credits charged for this request; equal to the number of matches returned (1 credit per match). example: 1 credits_exhausted: type: boolean description: >- `true` when the account ran out of credits before all matches could be billed; the unbilled matches are not returned. example: false '400': description: Invalid request content: application/json: schema: type: object required: - error properties: error: type: string enum: - missing emails - too_many_emails - invalid email - unexpected error description: >- `missing emails`: neither `emails` nor `email` was provided (or all entries were blank). `too_many_emails`: more than 1,000 addresses were submitted; see `max`. `invalid email`: at least one entry is not a valid email address. `unexpected error`: temporary error; safe to retry. max: type: integer description: Maximum batch size. Present only with `too_many_emails`. example: 1000 '401': description: Missing, malformed, or unknown API key content: application/json: schema: $ref: '#/components/schemas/AuthError' '402': description: Insufficient credits content: application/json: schema: $ref: '#/components/schemas/InsufficientCreditsError' '403': description: Service not enabled for this API key content: application/json: schema: $ref: '#/components/schemas/ServiceDisabledError' security: - api_key: [] components: schemas: AuthError: type: object required: - error properties: error: type: string enum: - missing_api_key - invalid_api_key_format - invalid_api_key description: >- `missing_api_key`: no key supplied. `invalid_api_key_format`: key does not match the expected format. `invalid_api_key`: key does not belong to any account. InsufficientCreditsError: type: object required: - error properties: error: type: string enum: - insufficient_api_credits required: type: string description: Credits needed for this request. example: '1.0' remaining: type: string description: Credits currently remaining on the account. example: '0.0' ServiceDisabledError: type: object required: - error properties: error: type: string enum: - service_unavailable_for_key securitySchemes: api_key: type: apiKey in: header name: X-Api-Key description: >- Per-account API key. Also accepted as `Api-Key` or `Authorization: Bearer `. ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.