Postfix website screenshot

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
9.0/100 minimal ▬ flat Agent 0/100 human only Full breakdown ↓
scored 2026-08-05 · rubric v0.9.1
1 APIs
EmailMail ServerMTASMTPOpen SourceInfrastructure

Kin Score

Kin Score Kin Score How this is scored →
scored 2026-08-05 · rubric v0.9.1
Composite quality — 9.0/100 · minimal
Contract Quality 0.0 / 25
Developer Ergonomics 1.7 / 20
Commercial Clarity 0.0 / 20
Operational Transparency 1.4 / 13
Governance 0.0 / 12
Discoverability 5.9 / 10
Agent readiness — 0/100 · human only
Machine-Readable Contract 0 / 18
Agentic Access Contract 0 / 10
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
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.

Postfix SMTP

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 pu...

Security Posture 2

Authentication, domain security, vulnerability disclosure, and trust-center signals.

Postfix Domain Security

TLSv1.3 · DNSSEC

SECURITY

Postfix Vulnerability Disclosure

security.txt · contact published

SECURITY

Resources

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)

apis.yml Raw ↑ 
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
url: https://raw.githubusercontent.com/api-evangelist/postfix/refs/heads/main/apis.yml
created: '2026-05-11'
modified: '2026-05-11'
specificationVersion: '0.19'
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