DB mil

Hi I am trying to configure DM mail on gmail.I have configured but cannot send test email.It gives me below errors.

The mail could not be sent to the recipients because of the mail server failure. (Sending Mail using Account 3 (2017-08-27T13:55:43). Exception Message: Cannot send mails to mail server. (The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. Learn more at).