Postfix

Postfix is a free, open source mail transfer agent (MTA) originally written by Wietse Venema at IBM Research as a fast, secure, and easy-to-administer alternative to Sendmail. It runs on UNIX-like systems including Linux, BSD, and macOS, routing and delivering email over SMTP with extensive support for TLS, SASL, DKIM/SPF/DMARC integration, content filtering, and policy delegation. Postfix is administered via configuration files (main.cf, master.cf) and command-line tools rather than a public HTTP API, and is one of the most widely deployed mail servers on the internet.

Postfix publishes 1 API on the APIs.io network. Tagged areas include Email, Mail Server, MTA, SMTP, and Open-Source.

Postfix’s developer surface includes documentation and 9 more developer resources.

🌐 Visit website 📡 Source on GitHub

9.9/100 minimal ▬ flat Agent 0/100 human only Full breakdown ↓
scored 2026-08-25 · rubric v0.14.0

1 APIs

EmailMail ServerMTASMTP Open-Source Infrastructure

Kin Score

Kin Score How this is scored →
scored 2026-08-25 · rubric v0.14.0

Composite quality — 9.9/100 · minimal

Contract Quality 0.0 / 25

Developer Ergonomics 1.9 / 20

Access Clarity 0.0 / 20

Operational Transparency 2.1 / 13

Contract Governance 0.0 / 12

Discoverability 5.9 / 10

Agent readiness — 0/100 · human only

Machine-Readable Contract 0 / 18

Agentic Access Contract 0 / 10

Documented Reversibility 0 / 6

MCP Server 0 / 12

Machine-Readable Auth 0 / 10

Idempotency 0 / 9

Stable Error Semantics 0 / 8

Request/Response Examples 0 / 7

Rate-Limit Signaling 0 / 7

Typed Event Surface 0 / 6

Agent Skills 0 / 5

Well-Known Catalog 0 / 4

Consent & Bot Identity 0 / 3

A2A Agent Card 0 / 8

Dry-Run / Simulate Mode 0 / 4

Delegated User Identity 0 / 6

Protected Resource Metadata 0 / 5

Registration Without a Human 0 / 6

Agentic Commerce Surface 0 / 5

Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. This rating is computed from github.com/api-evangelist/postfix: open an issue to ask a question, or submit a pull request to add artifacts. Want it done for you? Prioritized profiling — $2,500 →

APIs 1

Individual APIs this provider publishes, each with its own machine-readable definition.

Documentation 1

Reference material describing how the API behaves

Documentation

Documentation

Build 1

SDKs, sample code, and the tooling you integrate with

Source Code

Source Code

Access & Security 3

Authentication, authorization, and security posture

VulnerabilityDisclosure

VulnerabilityDisclosure

DomainSecurity

DomainSecurity

Security

Security

Commercial 1

Pricing, plans, and the legal terms of use

License

License

Company 1

The organization behind the API

Website

Website

Other 3

Properties that don't map to a standard resource type

Download

Download

Mailing Lists

Mailing Lists

Wikipedia

Wikipedia

Source (apis.yml)

aid: postfix
name: Postfix
description: Postfix is a free, open source mail transfer agent (MTA) originally written by Wietse Venema at IBM Research
  as a fast, secure, and easy-to-administer alternative to Sendmail. It runs on UNIX-like systems including Linux, BSD, and
  macOS, routing and delivering email over SMTP with extensive support for TLS, SASL, DKIM/SPF/DMARC integration, content
  filtering, and policy delegation. Postfix is administered via configuration files (main.cf, master.cf) and command-line
  tools rather than a public HTTP API, and is one of the most widely deployed mail servers on the internet.
type: Index
accessModel:
  pricing: unknown
  onboarding: unknown
  trial: false
  try_now: false
  public: false
  label: Unknown
  confidence: low
  source: []
  generated: '2026-07-22'
  method: derived
image: https://kinlane-images.s3.amazonaws.com/shared/apis-json/icons/postfix.png
tags:
- Email
- Mail Server
- MTA
- SMTP
- Open-Source
- Infrastructure
tags_raw:
- Email
- Mail Server
- MTA
- SMTP
- Open Source
- Infrastructure
url: https://raw.githubusercontent.com/api-evangelist/postfix/refs/heads/main/apis.yml
created: '2026-05-11'
modified: '2026-05-11'
specificationVersion: '0.23'
apis:
- aid: postfix:smtp
  name: Postfix SMTP
  description: Postfix implements SMTP (RFC 5321) for sending and receiving electronic mail, with submission (port 587), SMTPS
    (port 465), and standard SMTP (port 25) endpoints. There is no public HTTP/REST API; integration is via SMTP protocol,
    configuration files, milter (mail filter) hooks, and policy daemons.
  humanURL: https://www.postfix.org/documentation.html
  baseURL: smtp://localhost:25
  tags:
  - SMTP
  - Email
  - Mail Server
  - Protocol
  properties:
  - type: Documentation
    url: https://www.postfix.org/documentation.html
  - type: SMTP Specification
    url: https://datatracker.ietf.org/doc/html/rfc5321
  - type: Configuration Reference
    url: https://www.postfix.org/postconf.5.html
  - type: Milter Protocol
    url: https://www.postfix.org/MILTER_README.html
common:
- type: VulnerabilityDisclosure
  url: security/postfix-vulnerability-disclosure.yml
- type: DomainSecurity
  url: security/postfix-domain-security.yml
- type: Website
  url: https://www.postfix.org
- type: Documentation
  url: https://www.postfix.org/documentation.html
- type: Download
  url: https://www.postfix.org/download.html
- type: Source Code
  url: https://github.com/vdukhovni/postfix
- type: Mailing Lists
  url: https://www.postfix.org/lists.html
- type: Security
  url: https://www.postfix.org/security.html
- type: License
  url: https://www.postfix.org/license.html
- type: Wikipedia
  url: https://en.wikipedia.org/wiki/Postfix_(software)
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com

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