Service & Web UI

The Papercut SMTP Service is an optional background component that receives email even when the desktop app isn't running — as a Windows Service or a Docker container — and includes a browser-based UI for viewing messages.

The service is optional

For normal desktop use, the Papercut app alone is a complete SMTP server and viewer. Install the service for always-on setups, shared dev servers, or headless environments.

Web UI

The service serves a web interface at http://localhost:8080 by default:

Install as a Windows Service

1. Download Papercut.Smtp.Service.*.zip (x64, x86, or ARM64) from the latest release
2. Extract it anywhere
3. Run the install script as administrator:
4. install-papercut-service.bat (double-click), or
5. .\install-papercut-service.ps1 (PowerShell)

The service installs with automatic startup and starts immediately. To uninstall, run uninstall-papercut-service.bat / .ps1.

You can also run it as a plain console app — just execute Papercut.Service.exe.

Configuration

The service needs no manual configuration: when the desktop app and service run on the same machine, they synchronize settings automatically — change the SMTP port in the desktop Options and the service follows. Rules sync the same way.

For manual configuration, the service uses layered files (highest priority first):

File	Purpose
Papercut.Service.Settings.json	User settings — UI changes are saved here (SMTP IP, Port, etc.)
rules.json	Persisted rules
appsettings.Production.json	Docker/production overrides (non-privileged ports)
appsettings.json	Baseline defaults (SMTP port 25, IP Any)

Restart the service after manual edits.

Common changes

SMTP port — Papercut.Service.Settings.json:

{ "Port": "2525" }

Web UI binding — appsettings.json Urls setting:

{ "Urls": "http://localhost:8080" }

Use http://0.0.0.0:8080 to listen on all interfaces — but read the warning below.

Path prefix (reverse proxy / ingress) — serve the web UI under e.g. /webmail:

{ "HttpPathPrefix": "/webmail" }

Network exposure

When binding to 0.0.0.0, +, *, or a LAN IP, the web UI is reachable from other machines — and Papercut has no built-in authentication. Use firewall rules or a reverse proxy with auth in front of it.

API

The web UI is backed by a small HTTP API (/api/messages, etc.) you can script against — handy for asserting "an email was sent" in end-to-end tests. Explore the endpoints via your browser's dev tools on the web UI.

For AI agents and coding assistants, the service can also expose these operations over the Model Context Protocol — see MCP Server.