Not able to send the email on digital ocean

I don’t see that message posted above. I suspect that means that inmotion hosting doesn’t want you to use their SMTP server to send what it considers “mass emails.” You can ask them about the error. We cannot know.

You should probably use one of the recommended mail providers like Mailgun.

See discourse/docs/INSTALL-cloud.md at main · discourse/discourse · GitHub for how you should install Discourse. When you’re ready to reconfigure and use a different mail server, try doing this:

cd /var/discourse
./discourse-setup