Finally I was able to install the discourse with lots of learning.
- I was using the inmotion SMTP server and which doesnt allow the external email messaging. As suggested by forum members, utilised mailgun
- It is important to follow all the mailgun setup steps. It will ask you to add DNS records on the main domain and will authenticate. This may take 15/20 mins.
- Even after that, the discourse didnt worked. I killed the droplet multiple time.
- I noticed the my subdomain records were having old IP address. Cleaned up all the subdomain records (DNS Zone).
- Finally the email was received and after validating the link - 14 step wizard appeared.
The forum is worth all the effort and very happy for that 