BoltMail
Is it possible to resend an email to a contact list but only to the contacts that have joined after I sent it first?
Yes you can. Here's what you do:

1. Select the newsletter and send it as normal.
2. You can then use the "Filter" option and "Filter by date subscribed" This will give you a date field that you can select.
3. You select the date that you want to filter by, so it would be something like: Contacts that have subscribed after 20 Oct 2007.
4. Send the newsletter as per normal. It will only be sent to those that have subscribed after a particular date.

This will only send the emails to people who have subscribed after you have sent the email the first time.

Another alternative to this is to create an autoresponder instead of an email campaign. You can then set the autoresponder to be sent immediately after subscription and make sure you select to send to existing contacts.

What this will do is send the email to all the current contacts on your contact list and then will send to anyone who signs up after.