smtp4dev Email & SMTP Testing on Ubuntu 24.04 | 24/7 Support by cloudimg

smtp4dev is a fake, developer focused SMTP server with a modern web interface. It runs a fake SMTP server that catches every message your application sends, stores each one, and shows it in a web UI where you can read the HTML, plain text and raw source, inspect headers and attachments, and run HTML validation and compatibility checks. Because smtp4dev never delivers mail externally, it is completely safe to point development and staging applications at it: nothing ever reaches a real inbox. A built in IMAP server also lets a standard mail client browse the captured messages.

The cloudimg image installs the pinned smtp4dev 3.15.0 release on the ASP.NET Core 10 runtime and runs it as a dedicated smtp4dev system user under systemd. The web UI and REST API are fronted by nginx on port 80 with the WebSocket upgrade the live message list uses, and protected by HTTP Basic Auth whose password is generated uniquely on the first boot of every VM. The SMTP listener is exposed on port 25 for your applications and the IMAP server on port 143, the SQLite message store lives on a dedicated 20 GiB Azure data disk captured into the image, and an unauthenticated /healthz endpoint is provided for Azure Load Balancer probes. Backed by 24/7 cloudimg support.

Licensing - BSD-3-Clause, FREE. No per-message or per-seat fee. The cloudimg charge (0.04 USD per vCPU/hour) covers packaging, security patching, image maintenance and 24/7 expert support.