Can I resend an email to only those who haven't opened a message the first time?

Yes, but only if you are using Individual Measurement Mode.

  1. Go to the Metrics page for the message and click on the Didn't Open metric on the bottom left-hand side. This will open a data grid of contacts who have not responded. 
  2. Select all of the Contacts by placing a checkmark in the select all box.  
  3. Select Actions > New Message.   This will generate a new email message with the selected individuals in the To: field as a mailing list.  

You may now send a follow up message to those individuals who did not open your message.  If you want to resend the original message, you'll need to copy and paste it into this new message.