smtp4dev - Fake SMTP Server & Email Testing UI by cloudimg

This is a repackaged open source software product wherein additional charges apply for cloudimg support services.

Overview smtp4dev is a fake SMTP server for development and testing, built on the widely used open-source smtp4dev project (over 3,000 GitHub stars). It accepts the mail your applications send, stores it locally, and presents every captured message in a modern web UI inbox instead of delivering it to real recipients. That makes it safe to point a development, test or staging environment straight at it: nothing escapes to real mailboxes, and you can see exactly what your application would have sent. This image delivers smtp4dev fully installed and running behind an nginx reverse proxy, so a mail-testing console is serving within minutes of launch. The current release available is smtp4dev 3.15.0.

Why Choose This Image

• Self-hosted with no per-seat or per-message fees: it runs entirely in your AWS account at EC2 cost alone plus support, and sensitive test data never leaves your infrastructure.
• Production-grade security out of the box: unlike a bare mail sink that ships with no authentication, every instance generates a unique web password on first boot and proves it before recording it.
• IMAP support included: browse captured mail from any standard mail client, not just the web UI.
• Dedicated resizable data disk: captured mail persists in SQLite on its own EBS volume, independently resizable and separate from the operating system disk.

Application Stack smtp4dev is an ASP.NET Core application running under systemd as a dedicated unprivileged system user. It accepts SMTP on port 25 and IMAP on port 143, and serves its web UI and REST API on the loopback interface behind nginx on port 80, with the WebSocket upgrade its live-updating message list needs already configured. The .NET runtime is installed from the operating system's own package archive, so routine system updates keep the runtime patched rather than freezing it inside the application bundle. Captured mail is stored in a SQLite database on a dedicated data disk, separate from the operating system disk and independently resizable.

Catch And Inspect Every Message Point your application's SMTP settings at this instance on port 25 and smtp4dev captures everything it sends. The web UI lists messages as they arrive in real time and lets you view the rendered HTML, the plain-text part and the raw source, download and inspect attachments, read every header, and run smtp4dev's HTML validation to see which email clients would struggle with your markup. A REST API exposes the same message store so automated integration tests can assert that a message was sent and check its contents. Because smtp4dev also speaks IMAP, you can additionally browse captured mail from any standard mail client.

Secure First Boot On the first boot of your instance a one-shot service generates a web password unique to that instance, writes it into an override configuration file readable only by the service account, and starts smtp4dev with HTTP basic authentication required for both the web UI and the REST API. It then proves the result before recording anything: it confirms that an unauthenticated request is refused, that a wrong password is refused, and that the newly generated password is accepted, both directly and through the reverse proxy. Only then does it write the credentials file and mark first boot complete, so a failed rotation retries on the next boot rather than leaving an instance open. No shared or default credentials ship in the image, and the health endpoint used by load balancers stays open while the UI and API require the generated password.

Getting Started Launch the image with a security group allowing inbound TCP on ports 25 (SMTP), 143 (IMAP) and 80 (HTTP), SSH in to read the generated password from the root-only credentials file, then sign in to the web UI and point your application's SMTP settings at port 25 to watch messages appear instantly. A built-in health endpoint answers on the reverse proxy for load-balancer checks, and SMTP intake is left open so applications under test can send without credentials.

Use Cases Inspect the mail your application sends from development and staging without any risk of it reaching real recipients. Debug transactional email templates, HTML rendering and attachments before they go out. Give QA and support teams a shared inbox for verifying sign-up, password-reset and notification flows. Wire the REST API into automated integration tests that assert a message was sent.

cloudimg Support 24/7 technical support by email and live chat. Help with deployment, HTTPS and reverse-proxy configuration, SMTP and IMAP integration, storage and upgrade planning.

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