Fastmail

Fastmail provides secure, private email and calendar services for individuals and businesses. Founded in 1999, Fastmail emphasizes data protection, user privacy, and a feature‑rich experience with powerful filtering, custom domains, and cross‑platform synchronization. Their service includes robust spam protection, two‑factor authentication, and a focus on delivering a fast, reliable email platform without advertising or data mining. Fastmail also offers business plans with administrative controls, migration tools, and dedicated support, catering to professionals who need secure communication and reliable uptime.

Fastmail is listed with 1 API on the APIs.io network. Tagged areas include Email, Privacy, Security, Business, and Cloud.

Fastmail’s developer surface includes getting-started guide, documentation, API reference, support, engineering blog, pricing, and 19 more developer resources.

🌐 Visit website 📡 Profile data on GitHub

28.8/100 thin ▼ -9.3 Agent 18/100 agent aware Heartbeat 100/100 alive Full breakdown ↓
scored 2026-11-06 · rubric v0.27.0 · Show this score on your site →

AccessPaid

1 API

Email Privacy Security Business Cloud

Kin Score

Kin Score How this is scored →
scored 2026-11-06 · rubric v0.27.0

Composite quality — 28.8/100 · thin

Contract Quality 0.0 / 21

Developer Ergonomics 5.1 / 17

Access Clarity 8.1 / 17

Operational Transparency 3.2 / 11

Contract Governance 1.9 / 10

Discoverability 4.9 / 9

Regulatory Posture 4.0 / 15

Agent readiness — 18/100 · agent aware

Machine-Readable Contract 0 / 18

Agentic Access Contract 0 / 10

Documented Reversibility 0 / 6

MCP Server 0 / 12

Machine-Readable Auth 10 / 10

Idempotency 0 / 9

Stable Error Semantics 0 / 8

Request/Response Examples 0 / 7

Rate-Limit Signaling 7 / 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 6 / 6

Protected Resource Metadata 0 / 5

Registration Without a Human 6 / 6

Agentic Commerce Well-Known Document 0 / 5

Pagination 5 / 5

Distinct Operations 3 / 3

MCP Tool Quality 6 / 6

Regulatory Posture applies to this provider. Its tags matched the Horizontal (data, software, accessibility, platform) regime, so Regulatory Posture carries 15 points of the composite. If this regime is wrong for your business, say so on your provider repo — the applicability map is public and we will correct it.

Create-or-Update Ergonomics could not be measured. We hold no machine-readable contract for this provider to read, so there is nothing to measure a write surface against. Excluded rather than scored zero: never-measured and measured-empty are different facts. Publishing an OpenAPI is what makes this facet — and several others — scorable at all.

The six quality facets above are damped to 85 points between them, because the conditional facet above carries the other 15. That is why each facet's contribution is shown against a damped maximum: raising a quality facet moves the composite by 85% of its nominal weight, not 100%. The full arithmetic is at apis.io/rating/.

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Agent readiness — checks not met, largest first (exact, from this profile):

Machine-Readable Contract +18 pts — api_specs includes an OpenAPI document
MCP Server +12 pts — deployment.mode + probe verdict on the mcp/ manifest, not the pointer; an unprobed slug falls back to authorship
Agentic Access Contract +10 pts — agentic_access artifact present (x-agentic-access), graded by author
Idempotency +9 pts — OpenAPI mutating operations declare an idempotency key — a header, a request-body property, or a named de-duplication token whose own description says so (verified); else common[].type matches /idempoten/i (documented)
Stable Error Semantics +8 pts — OpenAPI $refs a shared error schema across 4xx/5xx responses (verified), else common[].type includes ErrorCatalog / ErrorCodes / DeclineCodes
A2A Agent Card +8 pts — a2a/-a2a.yml manifest, graded on conformance.grade against A2A 1.0.0

9 more unmet checks in the Agent Readiness table above.

Kin Score — facets with the most composite points still available (weight × headroom):

Contract Quality scores 0.0 — up to +25.0 composite points
Developer Ergonomics scores 29.8 — up to +14.0 composite points
Access Clarity scores 47.4 — up to +10.5 composite points

Each check links to what satisfies it. Publish the artifact, or tell us where it already lives, and the score moves on the next scoring run.

Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. Every facet and dimension name above is a link: it opens that measurement's own page — what it means, the exact checks that feed it, how the whole catalog distributes on it, and the providers at the top of it. This rating is computed from the provider profile at artifacts.apis.io/fastmail/apis.yml: open an issue on github.com/api-evangelist/fastmail to ask a question or point us at an artifact you publish. Submit an artifact on GitHub — free → Manage your own listing — the Influence plan, $499/mo →

Standards implemented 1

Standards this provider implements or carries. De facto ones are profiled and measured by the API Commons; formal ones come from the standards directory and are linked by the provider's own tags. The evidence column says how each claim was established — not that it was made.

Dynamic Client Registration

measured — observed by APIs.io (published)

APIs 1

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

Fastmail API

Fastmail email service API documented at the developer portal.

Fastmail API pricing

Prices published by Fastmail, read 2026-10-14 from www.fastmail.com/pricing/us/.

Plan	Price
Individual	$6 per month
Duo	$10 per month
Family	$14 per month

Plan details, limits and sources →

Rate limits

website IP throttling: no more than 10,000 requests and 200M of data per 10 minutes

Rate-limit details →

Pricing Plans 1

Published pricing tiers and plan structures.

Fastmail Plans Pricing

3 plans

PLANS

Rate Limits 1

Documented rate limits and quota policies.

Fastmail Rate Limits

1 limits

RATE LIMITS

Security Posture 2

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

Fastmail Domain Security

TLSv1.3 · HSTS · DMARC

SECURITY

Fastmail Vulnerability Disclosure

security.txt · contact published

SECURITY

Resources

Get Started 2

Portal, sign-up, and the first successful call

GettingStarted

GettingStarted

DeveloperPortal

DeveloperPortal

Documentation 2

Reference material describing how the API behaves

Documentation

Documentation

APIReference

APIReference

Agent Surfaces 1

MCP servers, agent skills, and machine-readable catalogs

WellKnown

WellKnown

Design & Contract 1

Pagination, idempotency, versioning, errors, and events

Conformance

Conformance

Build 3

SDKs, sample code, and the tooling you integrate with

SDKs

SDKs

Packages

Packages

GitHubOrganization

GitHubOrganization

Access & Security 6

Authentication, authorization, and security posture

SecurityTxt

SecurityTxt

SecurityTxt

Security

VulnerabilityDisclosure

VulnerabilityDisclosure

DomainSecurity

DomainSecurity

Operate 2

Status, limits, changes, and where to get help

RateLimits

RateLimits

Support

Support

Commercial 4

Pricing, plans, and the legal terms of use

Plans

Pricing

TermsOfService

PrivacyPolicy

Company 2

The organization behind the API

Website

Website

Blog

Blog

Other 2

Properties that don't map to a standard resource type

Hosts

Hosts

Vendors

Vendors

Source (apis.yml)

aid: fastmail
name: Fastmail
accessModel:
  pricing: paid
  onboarding: unknown
  trial: false
  try_now: false
  public: false
  label: Paid
  confidence: medium
  probe_state: unreadable
  source:
  - plans
  - rate-limits
  - security
  generated: '2026-11-06'
  method: derived
image: https://www.fastmail.com/assets/images/opengraph/Fastmail-OG.png
description: Fastmail provides secure, private email and calendar services for individuals and businesses. Founded in 1999,
  Fastmail emphasizes data protection, user privacy, and a feature‑rich experience with powerful filtering, custom domains,
  and cross‑platform synchronization. Their service includes robust spam protection, two‑factor authentication, and a focus
  on delivering a fast, reliable email platform without advertising or data mining. Fastmail also offers business plans with
  administrative controls, migration tools, and dedicated support, catering to professionals who need secure communication
  and reliable uptime.
url: https://raw.githubusercontent.com/api-evangelist/fastmail/refs/heads/main/apis.yml
x-type: company
x-source: harvest:tag-qc
x-tier: profiled
x-tier-reason: enrichment pass 2026-10-14 (modular-v1; was harvest)
specificationVersion: '0.20'
created: '2026-10-13'
modified: '2026-10-13'
tags:
- Email
- Privacy
- Security
- Business
- Cloud
maintainers:
- FN: Kin Lane
  email: kin@apievangelist.com
- FN: APIs.json
  email: info@apis.io
common:
- type: RateLimits
  url: rate-limits/fastmail-rate-limits.yml
- type: Plans
  url: plans/fastmail-plans-pricing.yml
- type: Conformance
  url: conformance/fastmail-conformance.yml
- type: SecurityTxt
  url: well-known/fastmail-security.txt
- type: SecurityTxt
  url: well-known/fastmail-app-security.txt
- type: SecurityTxt
  url: well-known/fastmail-api-security.txt
- type: WellKnown
  url: well-known/fastmail-well-known.yml
- type: Hosts
  url: hosts/fastmail-hosts.yml
- type: Vendors
  url: vendors/fastmail-vendors.yml
- type: SDKs
  url: packages/fastmail-packages.yml
- type: Packages
  url: packages/fastmail-packages.yml
- type: Security
  url: https://www.fastmail.com/features/security/
- type: GettingStarted
  url: https://www.fastmail.com/blog/why-replication-took-time-to-setup/
- type: GitHubOrganization
  url: https://github.com/fastmail
- type: VulnerabilityDisclosure
  url: security/fastmail-vulnerability-disclosure.yml
- type: DomainSecurity
  url: security/fastmail-domain-security.yml
- type: Website
  url: https://www.fastmail.com
- type: DeveloperPortal
  url: https://www.fastmail.com/dev/
- type: Documentation
  url: https://www.fastmail.com/dev/
- type: APIReference
  url: https://www.fastmail.com/dev/
- type: Support
  url: https://fastmail.help/
- type: Blog
  url: https://www.fastmail.com/blog/
- type: Pricing
  url: https://www.fastmail.com/pricing/
- type: TermsOfService
  url: https://www.fastmail.com/policies/terms-of-service/
- type: PrivacyPolicy
  url: https://www.fastmail.com/policies/privacy/
apis:
- name: Fastmail API
  description: Fastmail email service API documented at the developer portal.
  humanURL: https://www.fastmail.com/dev/
  baseURL: null
  aid: fastmail:fastmail-api
x-coverage:
  state: unreadable
  reason: js-rendered-docs
  detail: Developer portal returns HTML pages without a machine‑readable OpenAPI spec.
  evidence:
  - url: https://api.fastmail.com/openapi.json
    status: 200
  checked: '2026-10-14'
x-enrichment:
  date: '2026-10-14'
  status: enriched
  artifacts_added: 15
  pass: modular-v1
  engine: identity=local,contract=local,surfaces=local,docs=local,regulatory=local

Fastmail API — frequently asked questions

Does Fastmail have an API?

Yes. APIs.io lists 1 API from Fastmail, including Fastmail API.

How much does the Fastmail API cost?

Fastmail publishes its prices; its Individual plan is $6 per month as of 2026-10-14. APIs.io lists 3 pricing plans for Fastmail, with each plan's price, limits and inclusions under Pricing on this page.

Is the Fastmail API ready for AI agents?

Fastmail has a Kin Score of 28.8 out of 100 (thin) and an Agent Readiness score of 17.6 (agent-aware), scored by API Evangelist on 2026-11-06.

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get_provider_evidenceHow each part of their score was established. Free — the basis for a claim should not sit behind it.
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