This appears to be a regression in Mailer 1.24. I just updated that plugin this morning. If I go to Manage Jenkins -> Configure System -> Email notification -> Advanced -> Test configuration by sending test e-mail, the test fails with:

Failed to send out e-mail

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 r14sm33254971qke.47 - gsmtp

If I downgrade to the 1.23 version of Mailer, and don't change my configuration at all, then the test email is sent successfully.

Email configuration:

SMTP server: smtp.gmail.com

Default user e-mail suffix: blank

Use SMTP Authentication: true

User Name and Password: set correctly

Use SSL: true

SMTP Port: 465

Reply-To Address: no-reply@allworx.com

Charset: UTF-8