[Java Mail] Caused by: javax.mail.AuthenticationFailedException: 534-5.7.9 Application-specific password required.

Problem
I am writing a mail sending function by Java Mail API, and using gmail mail server as my smtp server. But as I try to run my testing code, it throw this exception:

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Caused by: javax.mail.AuthenticationFailedException: 534-5.7.9 Application-specific password required. Learn more at 534 5.7.9 https://support.google.com/accounts/answer/185833 xn8sm19248891pab.15 - gsmtp at com.sun.mail.smtp.SMTPTransport$Authenticator.authenticate(SMTPTransport.java:826) at com.sun.mail.smtp.SMTPTransport.authenticate(SMTPTransport.java:761) at com.sun.mail.smtp.SMTPTransport.protocolConnect(SMTPTransport.java:685) at javax.mail.Service.connect(Service.java:295) at org.springframework.mail.javamail.JavaMailSenderImpl.connectTransport(JavaMailSenderImpl.java:501) at org.springframework.mail.javamail.JavaMailSenderImpl.doSend(JavaMailSenderImpl.java:421) ... 4 more

How-To
You can go to https://support.google.com/accounts/answer/185833 to check the root cause.
Google asks you to generate an application specific password instead of your password.


Then I can send email via gmail mail server successfully.