Grails mail.debug not producing any output on tomcat9

Users have reported they don't receive mails. To assist them I need to debug the mails on the test environment. However, mail.debug doesn't produce any output. It works fine on my Dev Environment but I need to do this on the test environment as the e-mail adress in question has IP restrictions on it. My config file is as followed:

grails:
mail:
    disabled: "false"
    overrideAddress: "xxx"
    host: "smtp-relay.gmail.com"
    port: 465
    username: "xxx"
    password: "xxx"
    props:
        mail.smtp.auth: "true"
        mail.smtp.socketFactory.port: "465"
        mail.smtp.socketFactory.class: "javax.net.ssl.SSLSocketFactory"
        mail.smtp.socketFactory.fallback: "false"
        mail.smtp.ssl.enable: "true"
        mail.debug: "true"
grails.plugin.springsecurity.ui:
    register:
        emailFrom: "xxx"
        emailSubject: "xxx"
    forgotPassword:
        emailFrom: "xxx"
        emailSubject: "xxx"

Please note that all the entries marked with "xxx" are correctly configured, I just masked them here for security reasons.

It's grails version 3.3.4 deployed on Tomcat 9, Java Version is 8.

I also tried passing

-Dmail.debug=true

and all the log levels are set to DEBUG.

to the Java VM. However, the log produces absolutely nothing regarding mails.

Is there anything I can configure to get some output?

Solution

Add logger("grails.plugins.mail", DEBUG) to your grails-app/conf/logback.groovy file so it looks something like this at the bottom:

def targetDir = BuildSettings.TARGET_DIR
if (Environment.isDevelopmentMode() && targetDir != null) {
    appender("FULL_STACKTRACE", FileAppender) {
        file = "${targetDir}/stacktrace.log"
        append = true
        encoder(PatternLayoutEncoder) {
            pattern = "%level %logger - %msg%n"
        }
    }
    logger("StackTrace", ERROR, ['FULL_STACKTRACE'], false)
}

logger("grails.plugins.mail", DEBUG)

root(ERROR, ['STDOUT'])

In Grails 5 and Grails 6 where the logback configuration is stored in an XML file (grails-app/conf/logback.xml), the same thing can be accomplished by adding <logger name="grails.plugins.mail" level="DEBUG"/>.