Kotlinmailer

Send emails from any Kotlin platform: a Ktor backend, an Android or iOS app, a CLI tool or even the browser.

Documentation · API reference · Live demo · Migrating from 1.x

Kotlinmailer is a Kotlin Multiplatform mail library, built on coroutines and DSLs. It has its own SMTP and JMAP clients and doesn't need Java Mail.

This project is a hard fork of SimpleKotlinMail, which is no longer actively maintained.

• build emails with a DSL, including HTML via kotlinx.html, attachments and inline images
• standards compliant MIME rendering (RFC 5322, 2045-2047, 2231, 6532)
• send emails via SMTP: STARTTLS, implicit TLS, AUTH PLAIN/LOGIN/XOAUTH2/OAUTHBEARER, pipelining, connection pooling
• send emails via JMAP (RFC 8620, RFC 8621), which also works in the browser
• no Java Mail dependency, only kotlinx libraries and Ktor

val mailer = smtpMailer("smtp.example.com") {
    credentials("john.doe@example.com", "app-password")
}

emailBuilder {
    from("John Doe <john.doe@example.com>")
    to("alice@example.com")
    subject = "Hello from Kotlin"
    text = "Sent from any platform!"
}.send(mailer)

dependencies {
    implementation("at.quickme.kotlinmailer:core:2.0.0")
    implementation("at.quickme.kotlinmailer:smtp:2.0.0") // and/or jmap, html
}

jmap needs a Ktor client engine, e.g. ktor-client-cio or ktor-client-js. See Modules for Maven and more details.

The demo is a Kobweb website that sends emails over JMAP straight from your browser, without a backend. SMTP can't work there, because browsers can't open TCP connections. The source is in demo.

Contributions are very welcome, whether it's code, documentation or a good bug report.

• Found a bug? Open a bug report.
• Missing a feature, e.g. one that 1.x had? Open a feature request, or 👍 an existing one.
• Want to send a pull request? For larger changes, please open an issue first so we can agree on the approach.

To work on the code you need JDK 21. Then:

./gradlew check                 # tests on every platform your machine supports, detekt and the API check
./gradlew apiDump               # after changing the public API, commit the updated api/ files
./gradlew :demo:kobwebStart -t  # run the demo at http://localhost:8080/Kotlinmailer/demo/ with live reload

• Protocol code goes into smtp or jmap. core stays dependency-light and compiles for every target.
• New behaviour needs tests, preferably in commonTest.
• When you change behaviour that users can see, update the docs in docs/Writerside.
• Commit messages follow Conventional Commits, e.g. fix(smtp): ... or docs: ....

More details are in the contribution guide.

Kotlinmailer is licensed under the Apache License 2.0.