SMTP 발송을 할때는 다음 두가지의 라이브러리가 있어야 한다.

• mail-api
  • https://mvnrepository.com/artifact/javax.mail/javax.mail-api/1.6.2
  • JavaMail API JAR
• activation
  • The JavaBeans(TM) Activation Framework is used by the JavaMail(TM) API to manage MIME data
  • https://mvnrepository.com/artifact/javax.activation/activation/1.1.1

참고

https://stackoverflow.com/questions/1630002/java-lang-noclassdeffounderror-javax-mail-authenticator-whats-wrong