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Troubleshooting

I don't see any emails

  1. Is Papercut running? The desktop app must be open (or the service installed) to receive email.
  2. Check the Logs view — you should see the SMTP server listening (e.g. 127.0.0.1:25). If another program grabbed the port, Papercut will say so; pick a different port in Options.
  3. Confirm your app's SMTP settings — host localhost, and the port must match Papercut's (default 25; Docker default 2525).
  4. Send a test email directly to isolate whether the problem is your app or Papercut: 
    Send-MailMessage -SmtpServer localhost -Port 25 -From "a@b" -To "c@d" -Subject "test" -Body "test"
  5. Sending from another machine, VM, or container? Papercut defaults to 127.0.0.1 — localhost only. Set the IP to Any in Options, and check your firewall.

"The IP and Port combination is in use"

Another program (often IIS SMTP, another mail catcher, or an antivirus proxy) is already listening on port 25. Change Papercut's port in Options, or stop the other program.

Do I need the Papercut Service?

No. The desktop app alone receives and displays email. The service is only for receiving email when the desktop app isn't running — see Service & Web UI.

HTML emails don't render / blank message view

The HTML view requires the WebView2 Runtime, preinstalled on current Windows. If it's missing, install it from Microsoft's WebView2 page and restart Papercut.

Emails send fine but my app errors on authentication or TLS

Papercut accepts any credentials, but TLS is off by default. If your app requires an encrypted connection, either disable TLS in the app's dev configuration or enable TLS in Papercut.

Where are my emails stored?

As .eml files on disk. In the desktop app, right-click a message → open its containing folder. The storage location is configurable in Options.

Docker: web UI loads but no emails arrive

Your app must send to the container's SMTP port (default 2525, or whatever you mapped) — not port 25 on localhost, unless you mapped -p 25:2525. From other containers in the same compose network, use the service name as host. See Docker.

Still stuck?

  • Check the Logs view (desktop) or container logs (docker logs papercut) for errors
  • Search existing issues
  • Open a new issue with your setup details and log output