BoltMail
How do I send a newsletter to contacts who have signed up since the last campaign was sent?
If you want to send an email campaign to contacts that have signed up after you have already sent it then you can make use of the application's filtering options.

To do this simply select to send the email campaign and remember to select 'Show Filtering Options'.

This will allow you to select the option of sending to all contacts on that contact list/s that have subscribed past a date that you select. Simply make this the date that you sent your email campaign and send it.

This will only send to those contacts that have signed up since you last sent your email.