Eblast Day Limit - How to re-send the email for the ones who didn't received it?

Eblast Day Limit - How to re-send the email for the ones who didn't received it?

Hi everyone!

Thank you for your all help in advance.

We sent a mass email for 2060 leads, but only 1000 were received.
Later we discover that we exceed the 1000 mass email leads per day limit.

My question is:

How now can I send the same email ONLY for the other half? 
How can I select only the ones who didn't receive the first one?

Thank you so much for your all help.