please provide more detailed specs on the question. For this question, its not that the quesion is not clear.....but still people would like to get more detailed question with all the gaps filled in.
So now with your answer :
Set up a variable count_files_deleted in your SSIS
Fill this variable up with the number of files deleted. (lets say from a script component or maybe a RowCount transformation etc.)
In your SenMail task, use an expression utilizing this variable count_files_deleted to create your MessageSource property for the SendMail task.