# SMTP

**Canonical:** https://apis.io/providers/smtp/  
**APIs profiled:** 2

Simple Mail Transfer Protocol (SMTP) is the foundational internet standard for transmitting electronic mail across networks. Defined in RFC 5321 (October 2008), SMTP uses a command-response model over TCP port 25 (or 587 for submission, 465 for SMTPS). It defines commands including EHLO, MAIL FROM, RCPT TO, and DATA, along with a comprehensive set of response codes. SMTP works in conjunction with RFC 5322 (Internet Message Format) which defines the structure of email messages.

## Kin Score — 14.0 / 100 (emerging)

Scored 2026-08-25 under rubric 0.14.0. Trend: flat (+0.0 from 14.0).

| Facet | Score |
|---|---|
| Discoverability | 59.3 |
| Contract Quality | 10.7 |
| Governance | 9.8 |
| Contract Governance | 9.8 |
| Operational Transparency | 7.9 |
| Developer Ergonomics | 0.0 |
| Commercial Clarity | 15.8 |
| Access Clarity | 15.8 |

## Agent readiness — 2.5 (human-only)

| Dimension | Value |
|---|---|
| Spec Presence | no |
| Agentic Access | no |
| Reversibility Documented | no |
| MCP Server | no |
| Auth Clarity | no |
| Idempotency | no |
| Error Semantics | no |
| OpenAPI Examples | no |
| Rate Limit Signal | documented |
| Event Surface Described | no |
| Agent Skills | no |
| Well Known Catalog | no |
| Consent Identity | no |
| Agent Card | no |
| Dry Run Mode | no |
| Delegated Identity | no |
| Protected Resource Metadata | no |
| Dynamic Client Registration | no |
| Agentic Commerce | no |

## Access

Freemium — onboarding: unknown, pricing: freemium, trial: no (confidence: medium).

## APIs (2)

- **RFC 5321 - Simple Mail Transfer Protocol** — RFC 5321 is the IETF standard defining the Simple Mail Transfer Protocol. It specifies the client-server protocol used to transmit email across the internet, including the comma...
- **RFC 5322 - Internet Message Format** — RFC 5322 defines the format of electronic mail messages transmitted via SMTP. It specifies the syntax for message headers (From, To, Subject, Date, etc.) and body structure. Wor...

## Security (1)

- **Smtp Domain Security** — TLSv1.3 · HSTS · DNSSEC · DMARC

## Plans (1)

- **Smtp Plans Pricing**

## Tags

SMTP, Email, Internet Standards, IETF, Messaging, Protocols, RFC 5321

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Profiled by [API Evangelist](https://apievangelist.com) and published on [APIs.io](https://apis.io/providers/smtp/). Scores are computed from the provider's own public artifacts under a published rubric.