Wpf application for sending mail from datagrid values which is fetched from the excel using epplus library

The question is made up of many moving parts.

Break it down into its individual units to make it easier for you to work with:

1. Service layer:
* sending mail - MS internal API or using 3rd party library; write code to send an email as a contained service
* data from MS Excel - use MS Interop, 3rd party tool, or other; write code to send an email as a contained service

2. UI Layer:
You can use with either WinForm or WPF UI System. You have chosen WPF, so now:
* code behind or MVVM design patterns - This will determine how you wire up the DataGrid. The DataGrid is just a way for the app to communicate with the user.

Google each part if you are unfamiliar with them. Get each part working individually and do the UI last.

If you get stuck for an individual part, not the whole app's needs, now in a question, outline:
1. what you are trying to do
2. your test code
3. what you have tried, any error codes, where have they occurred, what the debugger is telling you, etc ... then we are in a better position to help you.