Hello,
Thanks for the provided information.
It seems that you are specifying the google SMTP in Wazuh configuration <smtp_server>
smtp.google.com</smtp_server> but Wazuh does not handle the authentication to the SMTP's and it is the reason of using POSTFIX which you have already configured.
Having said that, you should use ` <smtp_server>localhost</smtp_server> and then restart the Wazuh manager(assuming that you have installed postfix in the same box as the Wazuh manager).
Hope this helps.
Regards,
Wali