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Sending mail via GMail using Kotlin and commons-mail library

· 3 min read
Dusan Odalovic

Continuing series of blog posts related to Kotlin, today we’ll together make a sample application showing us how we could automate email sending – using Kotlin programming language. Example is quite simple, and surely – you can enhance it with own features. Application mostly demonstrates compact Kotlin syntax, as well as full compatibility with Java or 3rd party libraries (in this case Apache commons-mail library).

Let’s first take a look at our script (scripts/mail/MailSender.kt):

package mail

import org.apache.commons.mail.DefaultAuthenticator
import org.apache.commons.mail.HtmlEmail
import java.net.URL

fun main(args: Array<String>) {
    val senderEmail = args[0]
    val password = args[1]
    val toMail = args[2]

    val email = HtmlEmail()
    email.hostName = "smtp.googlemail.com"
    email.setSmtpPort(465)
    email.setAuthenticator(DefaultAuthenticator(senderEmail, password))
    email.isSSLOnConnect = true
    email.setFrom(senderEmail)
    email.addTo(toMail)
    email.subject = "Test email with inline image sent using Kotlin"
    val kotlinLogoURL = URL("https://kotlinlang.org/assets/images/twitter-card/kotlin_800x320.png")
    val cid = email.embed(kotlinLogoURL, "Kotlin logo")
    email.setHtmlMsg("<html><h1>Kotlin logo</h1><img src=\"cid:$cid\"></html>")
    email.send()
}

Application input​

There are three input parameters required:

  • your GMail address
  • your GMail password
  • recipient's email address

Application dependencies​

Application requires having 3 libs on your classpath. You can either use build tool to help you automate that, or, in case you don’t want to depend on that – just download the libs listed below, and put them in lib directory.

  • activation-1.1.1.jar
  • commons-email-1.4.jar
  • javax.mail-1.5.2.jar

Application layout​

Application requires the following filesystem structure:

- project-root
  - scripts
    - mail
      - MailSender.kt
  - lib
    - activation-1.1.1.jar
    - commons-email-1.4.jar
    - javax.mail-1.5.2.jar

Compiling application (run from project root)​

kotlinc \
 -cp lib/activation-1.1.1.jar:lib/commons-email-1.4.jar:lib/javax.mail-1.5.2.jar \
 scripts/mail/MailSender.kt -include-runtime -d mailSender.jar

Running application (run from project root)​

java -cp "mailSender.jar:lib/\*" \
 mail.MailSenderKt \
 <YOUR-GMAIL-ADDRESS-HERE> <YOUR-GMAIL-PASSWORD-HERE> <RECIPIENT-MAIL-HERE>

In case you have enabled two factor authentication using your GMail account, you need to create application password here and use that as a password in command above.

Mail contain header and logo will be delivered to mail recipient you passed to java command above

That was all for today! Hope you liked it!