Hey Abhinaya, there are two issues with your config\vizalerts.yaml settings:
1. VizAlerts can't verify the certificate you are using to encrypt traffic for connections to your Tableau Server instance. So you can either set server.ssl to false for testing purposes, or server.certcheck to false (also for testing purposes, though this isn't as bad as simply turning ssl off!). If you have that working already, then point server.certfile at the filepath for your set of trusted CA certificates in .pem format.
2. The error email generated from the first error could not be sent because your SMTP server isn't accepting the username/password you set in smtp.user / smtp.password. Leaving both as "null" means no authentication is being used by the SMTP server, so don't send it any credentials. That's most likely what you need to do. If it doesn't work, ask your friends in IT what authentication method your SMTP server is using.
Tried all the steps mentioned above, Still throwing the below error .
MainThread - 2017-05-26 21:17:20 - [DEBUG] - get_trusted_ticket - NOT using SSL and NOT verifying cert
MainThread - 2017-05-26 21:17:22 - [ERROR] - get_trusted_ticket - URLError generating trusted ticket: [Errno 10061] No connection could be made because the target machine actively refused it Request details:
MainThread - 2017-05-26 21:17:22 - [INFO] - send_email - sending email: <smpt server name> ,<smtp from address>,<smtp to address>,None,None,ALERT: VizAlerts failed to execute properly, None
MainThread - 2017-05-26 21:17:22 - [ERROR] - quit_script - Unknown error-sending exception alert email: No suitable authentication method found.
MainThread - 2017-05-26 21:17:22 - [ERROR] - <module> - An unhandled exception occurred: Traceback
Well, you've got a new error on the first problem, at least. Check and make sure that your server name is spelled correctly in the vizalerts.yaml, and you should make it just the name, without any "http" in front. Also, ensure that you're running Tableau Server on port 80, since you turned SSL off. If you aren't, you can append ":41241" (or whatever your port is) to the end of the "server" config setting.
With the SMTP issue, I'd advise working with your IT team, if you've exhausted all the combinations of username / password / null that you can in the config.