Specific error:
AuthenticationFailedException: 535-5.7.8 Username and Password not accepted. Learn more at 535 5.7.8 https://support.google.com/mail/?p=BadCredentials o19sm9099443pjr.2 - gsmtp
Specific solutions:
Login gmail generate application code, configuration to jira email password.
Further reading:
https://community.atlassian.com/t5/Jira-questions/Using-Gmail-as-a-JIRA-Mail-Server/qaq-p/824782