The first thing you need to do is add this collection to the email, you need to change it to a string so that it can be added to the email. The way you've built it, you're only adding a value from one cell - the one from that column and current row. There is no official Utility action that can change collection to text.
The other way is to loop through collection [Emails Not Sent] and join the data from collection to a text data item. Then you can use that data item in the email that you're sending.
I'd like to suggest for you, to send emails using HTML mode. There are numerous advantages to that - you can use HTML formatting, hyperlinks, tables.