To relaunch a mail to the contacts that didn't opened their mail yet you can go through the next steps:

1. Go to the evaluation of the mail you want to resend to the contacts that didn't open their mail.
2. Click on the 'not opened' number to get the not openers list
3. Click on the 'Save as contact group' button and give the new group a name

The next step depends on what you want to do:

Send the same mail again:

1. Go to the evaluation section with the campaign items
2. Click on the 'relaunch' button
3. Select the created contact group in the To section
4. Complete the launch wizard

Send an other mail:

Launch a new campaign with the new mail to the created contact group