19:04:00 ERROR c.i.i.s.s.system.MailServiceImpl - >> Occur Exception: Failed messages: com.sun.mail.smtp.SMTPSendFailedException: 530 5.7.0 Must issue a STARTTLS command first. a11sm6769399pdj.54 - gsmtp
위의 메시지가 나타난다면, compile "com.sun.mail:javax.mail"
의존성을 추가하자.