Under the recipients section of marketing emails you can see the reasons for the Not Sent contacts. However, when I was looking at these and figuring out why the numbers were so high, I noticed that when you use the filter to break down the reasons for not sending, it didnt add up to the total not sent amount.
It turns out, the contacts where they werent sent to because they are non-marketing dont have their own filter or sit under the ‘Other’ category. I am suggesting that this becomes its own option to filter by, especially as the marketing/non-marketing feature becomes more readily used. It would have saved a lot of time trying to figure out where these contacts came from.