Hi Vinay,
The first step to send email campaigns via CleverTap is to integrate your email provider with us - We integrate with most email providers like SendGrid/Mandrill/Amazon and even support SMTP Settings. To integrate your email provider, you have to go to the settings section of your CleverTap dashboard and go to the "Integrate Email" section and add your account credentials.
Once you have set up your email account, you can automate an email campaign going out to your users by setting up the "Tackle App Uninstalls" Clever Campaign. All you have to do is give us the content and then emails will automatically be sent to your users (the email id your user sees will be the once you have integrated with us)
You can get list of people who have uninstalled your application by going to the "Find People" section of your dashboard and then downloading all the people who have uninstalled your application.
Cheers,
Support