Hi Sumit--sorry, I didn't see this until now. I'm not sure what could cause this error. My guess is that VizAlerts is having trouble talking to your SMTP server. Some things to try:
1. Double check the port number in the config\vizalerts.yaml file. Is your SMTP server accepting traffic on that port?
2. Ensure your local firewall allows traffic to the SMTP server, on the port you specified
3. Apply any outstanding Windows updates (I assume this is Windows)
4. Restart your machine
If those things don't work, post a log snippet from VizAlerts and we'll keep digging.