+1.

I got the same Authentication issue today on my new jenkins. I was confused why I got this error.

Then I compared with another jenkins which works properly. The only difference is the correct one use the mailer plugin 1.23 while the error one with 1.24.

I upgrade the plugin from 1.23 to 1.24, after that, I got the same error.

And it came to work again once I downgrade it back to 1.23

Both nodes run Jenkins ver. 2.176.2 on centOS 7.4

I too got the same issue with "smtp.gmail.com" while performing "Test Configuration" in Manage Jenkins --> Configure System --> Mail Settings

Jenkins Version 2.176.2 on Ubuntu 18.04 LTS and Mailer Plugin 1.24.

com.sun.mail.smtp.SMTPSendFailedException: 530-5.5.1 Authentication Required. Learn more at
530 5.5.1  https://support.google.com/mail/?p=WantAuthError j6sm15598012pfg.158 - gsmtp

	at com.sun.mail.smtp.SMTPTransport.issueSendCommand(SMTPTransport.java:2057)
	at com.sun.mail.smtp.SMTPTransport.mailFrom(SMTPTransport.java:1580)
	at com.sun.mail.smtp.SMTPTransport.sendMessage(SMTPTransport.java:1097)
	at javax.mail.Transport.send0(Transport.java:195)
	at javax.mail.Transport.send(Transport.java:124)
	at hudson.tasks.Mailer$DescriptorImpl.doSendTestMail(Mailer.java:613)
	at java.lang.invoke.MethodHandle.invokeWithArguments(MethodHandle.java:627)
	at org.kohsuke.stapler.Function$MethodFunction.invoke(Function.java:396)
	at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:408)
	at org.kohsuke.stapler.interceptor.RequirePOST$Processor.invoke(RequirePOST.java:77)
	at org.kohsuke.stapler.PreInvokeInterceptedFunction.invoke(PreInvokeInterceptedFunction.java:26)
	at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:212)
	at org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:145)
	at org.kohsuke.stapler.MetaClass$11.doDispatch(MetaClass.java:535)
	at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedD

same issue here. "Test configuration" is failing although emails are working fine. I tracked the issue down to wrong parameters send then hitting `Test configuration` button - parameters are not nested as they should be according to code: https://github.com/jenkinsci/mailer-plugin/blame/mailer-1.24/src/main/java/hudson/tasks/Mailer.java#L397

note that hitting "apply" sends parameters correctly.

I was facing exactly same issue that Zong Shen mentioned here but the challenge for me was downgrading the plugin since I didn't see downgrade plugin option next to the installed plugin. So, here's how I did it:

1. Download mailer-1.23.hpi from https://javalibs.com/artifact/org.jenkins-ci.plugins/mailer
    
   2. Goto jenkins -> Manage Jenkins -> Manage plugins -> Advanced -> Upload Plugin -> Choose downloaded file -> click on upload.
    
   3. Restart jenkins once upload is done. (It was showing that mailer is already installed, don't worry just restart jenkins)
    
   4. Check mailer version - it will be set to 1.23 now with an upgrade option available.
    
   Now, test mail works perfectly fine. Hope this helps someone who gets this issue.
    
   This is just a workaround. Some one please fix the issue with mailer plugin version 1.24

Only affects the "test email" feature, this code path isn't used for real emails.