Hi I have used another system that allows you to resend your email campaign to the email addresses in your list that haven't already received the email. This way you don't have to keep track of when users signed up vs. when you sent out your email. Can campaign monitor do the same?
With Campaign Monitor you can use the 'edit and resend' function to copy a sent campaign back to drafts. We don't have an automatic way to send it to people who haven't received it, but you can create a segment with a rule like "date added is after <date>".
See http://www.campaignmonitor.com/resources/entry/1695/creating-and-using-segments/ for help with segmenting. Then you could send the campaign to just those people.
Thanks for the quick reply!