Invalid Emails

We had a major RDS database problem last week and have been reimporting data bit by bit into a new database. 

I created 30K contacts, and then used external ID to give them all email addresses. 

Now when I go into individual user records an email address appears, but when I click on it it says 

"Error
Your user record does not have a valid email address"
 
Also if I try to send a mass email to the entire group it says I only have 7 valid emails instead of 30K