Mailroom

Mailroom is a Kotlin email composition and delivery library for server-side applications.

Features

• Framework-agnostic core for any Kotlin server app
• Type-safe HTML DSL with kotlinx.html
• Pluggable adapters for SMTP, SES, Resend, local, and testing
• Optional Ktor plugin and mailbox preview UI

Quick Start

Add the dependencies:

dependencies {
    implementation("dev.dela:mailroom-core:X.Y.Z")
    implementation("dev.dela:mailroom-smtp:X.Y.Z")
}

Configure, compose, and send:

val mailer = DefaultMailer(
    SmtpAdapter(
        SmtpConfig(
            host = "smtp.example.com",
            port = 587,
            username = System.getenv("SMTP_USERNAME"),
            password = System.getenv("SMTP_PASSWORD"),
            useTLS = true,
        ),
    ),
)

val result = mailer.deliver(
    email {
        from("noreply@example.com", "My App")
        to("user@example.com", "User Name")
        subject("Welcome")
        textBody("Thanks for signing up!")
    },
)

when (result) {
    is DeliveryResult.Success -> println("Sent: ${result.messageId}")
    is DeliveryResult.Failure -> println("Failed: ${result.reason}")
}

Documentation:

• Using Mailroom
• Creating a New Adapter

Available Adapters

• mailroom-smtp — SMTP adapter built on Jakarta Mail (Gmail, Mailgun SMTP, etc.).
• mailroom-ses — Amazon SES adapter using the AWS SDK for Kotlin.
• mailroom-resend — Resend HTTP adapter.
• mailroom-local — In-memory adapter for local development with mailbox storage.
• mailroom-test — Test adapter with assertion DSL for verifying sent emails.

Requirements

• Kotlin 2.1 or later
• JVM 17 or later
• Gradle 7.6.3 or later (built with Gradle 9.0)
• Coroutines support
• Ktor 3.2+ (only if using mailroom-ktor and mailroom-preview)

License

MIT License - see LICENSE for details.

Inspiration

Mailroom is inspired by Swoosh, the excellent email library for Elixir.