AD synchronizations changing e-mail address

I have some users that have AD account on our domain but their e-mail address are not ours. We have changed the e-mails to the correct e-mails in Servicedesk but after an AD sync it changed it back to our domain e-mail address. If you look at the User1 properties in AD they don't have an e-mail specified but the regular users do have the e-mail specified.  

What am I doing wrong?

Thanks

Jen