[Messaging.SingleEmailMessage].setToAddress(LIST<String>)

Hi.. Im trying to implement a scheduling job email alert for a task which is over due.. I'm getting this following error..

Method does not exist or incorrect signature: [Messaging.SingleEmailMessage].setToAddress(LIST<String>) at line 29 column 7

global void sendemail(User u, Task t)
{
Messaging.SingleEmailMessage email = new Messaging.SingleEmailMessage();
string[] toaddress = New String[] {u.Email};
email.setSubject('Task Almost Overdue');
email.setPlainTextBody(t.Subject + 'is due ' + t.ActivityDate + ' and needs some attention.');
email.setToAddress(toaddress);
Messaging.sendEmail(New Messaging.SingleEmailMessage[] {email});
}
}