Native local email testing for macOS

Catch emails before they go live.

Postkasten is a focused Mac app for previewing, inspecting and checking local developer emails before they reach real users. No account, no cloud, no fuss.

Download on the Mac App Store View SMTP setup
127.0.0.1 Port 1025 Local SMTP
Postkasten macOS app showing an inbox, email preview, SMTP status and compatibility checks
Local SMTP catcher

Quick setup

Point your app at Postkasten.

1

Start Postkasten

Open the Mac app and make sure the local SMTP catcher is running.

2

Use local SMTP

Configure your development app to send SMTP to 127.0.0.1 on port 1025.

3

Send a test email

Trigger a password reset, account confirmation, invoice or other transactional email from your local app.

Agent-friendly foundation

Built for today’s UI, prepared for automated workflows.

Postkasten 1.0 focuses on the native Mac workflow. Its core is kept separate so future CLI, local API and agent-assisted test flows can reuse the same local email engine.

Stable local SMTP target

Developers and tools can point test emails at 127.0.0.1:1025.

Testable core boundaries

SMTP capture, message storage, parsing and checks are kept out of SwiftUI views.

Future CLI and local API

Machine-readable commands and local API endpoints are planned as later clients of the same core.

Focused utility, not a suite

Everything needed for the local email loop.

Local SMTP catcher

Capture development emails on your Mac before they ever leave your machine.

Comfortable previews

Switch between rendered HTML, plain text, raw source and headers without hunting through logs.

Attachments

Review attachment names, types and sizes, then save or open files deliberately.

Setup snippets

Copy framework-ready SMTP settings for common stacks and get back to your app.

Risk hints

Surface likely email rendering and safety issues without pretending to replace real client testing.

Native Mac feel

A quiet SwiftUI app with menu bar status, launch at login and light/dark mode.

Fair indie pricing

One-time purchase via the Mac App Store.

Postkasten is a paid native Mac utility: simple to buy, useful offline and respectful of developer workflows.

Version 1.0

49 EUR

One-time purchase through the Mac App Store. No subscription for the local app.

  • Native macOS app
  • Local SMTP capture
  • Preview, headers and attachments
  • Basic rendering-risk hints
Download on the Mac App Store

Trust by design

Local means local.

Postkasten is not a cloud email QA platform. It is a local Mac app for a clear development workflow.

Emails stay on your Mac

No account, no cloud sync and no telemetry in the core product.

Honest compatibility language

Postkasten gives risk reports and likely issue hints, not fake Gmail or Outlook certainty.

Built for developers

Laravel, Rails, Symfony, Node and generic SMTP workflows are first-class setup paths.

Questions developers ask first

FAQ

No. The core product is a local macOS app. Captured development emails stay on your Mac.

No. Postkasten helps with local previews and likely issue hints. It does not claim exact rendering in Gmail, Outlook, Apple Mail or other external clients.

No. Postkasten is distributed through the Mac App Store, so purchase, updates and refunds stay in one familiar place.

Yes. The local app is designed to catch and inspect development emails on your Mac without an account or cloud service.

No. Captured emails are intended to stay local. Postkasten is not a cloud inbox, sync service or email delivery platform.

Yes. Any app that can send SMTP can use Postkasten. Built-in setup snippets cover Laravel, Rails, Symfony, Node/Nodemailer and generic SMTP.

Refunds for Mac App Store purchases are handled by Apple through the App Store purchase flow.

Support

Clear answers for daily use.

Postkasten is small on purpose. Support is just as clear: local SMTP setup, known limits and App Store purchase guidance.

Open support page

Refunds

Purchases and refunds run through Apple, not a custom Postkasten billing account.

Known limits

Postkasten gives local previews and compatibility hints. It does not provide real Gmail or Outlook screenshots.

Setup

Use local SMTP with 127.0.0.1 and port 1025 for supported development stacks.

Support

Need help with Postkasten?

For setup questions, support and product feedback, email the Postkasten support address.

Email support

Purchased through the Mac App Store? Refunds and purchase history are handled by Apple.