Does in past days include today?

Caroline,

In past 30 days filter I believe does NOT count today, but let's have Support confirm that.

Ok, I think I said this wrong the first time.

Not Was Sent Email is going to include anyone who was never sent the email in the past 30 days. Possibly it looks like if you just sent that email today, then using "30 days" isn't going to work. You could have used "In Past 1 Hour" but that might also not work unless the send command had been fully completed. Large runs will take longer to fully record.

If you wanted to specifically exclude the group you had previously emailed, you could also try Member of Smart Campaign NOT IN, assuming it was a single use batch campaign. 

Thanks Josh,

these "Not.." filters always confuse me. But I still think the "Not was sent email" was the filter I wanted? Send this email to anyone who was not sent the same email before.

I added the email to three different engagement programs, but then I also wanted to send the same email out manually afterwards to those who didn't receive it through the engagement programs. This is where I needed the Not was sent email filter. Or am I not getting it?