global class ContactEmailUpdateBatch implements Database.Batchable<sObject>
{

   global final String Query;
   
   global ContactEmailUpdateBatch(){
      
       Query='SELECT Email FROM Contact WHERE Email != null';

   }

   global Database.QueryLocator start(Database.BatchableContext BC){
       return Database.getQueryLocator(query);
   }

   global void execute(Database.BatchableContext BC, List<Contact> scope){                     

        List<Contact> contactsToUpdate = new List<Contact>();  
        EmailManager emailMgr = new EmailManager();
       
        for(Contact contact : scope)
        {
			emailMgr.sendMail(contact.Email, 'Subject', 'Body');
        }      

   }

   global void finish(Database.BatchableContext BC){

   }
}

public class EmailManager {
    // Public method
    public void sendMail(String address, String subject, String body) {
        // Create an email message object
        Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
        String[] toAddresses = new String[] {address};
        mail.setToAddresses(toAddresses);
        mail.setSubject(subject);
        mail.setPlainTextBody(body);
        // Pass this email message to the built-in sendEmail method 
        // of the Messaging class
        Messaging.SendEmailResult[] results = Messaging.sendEmail(
                                 new Messaging.SingleEmailMessage[] { mail });
        
        // Call a helper method to inspect the returned results
        inspectResults(results);
    }
    
    // Helper method
    private static Boolean inspectResults(Messaging.SendEmailResult[] results) {
        Boolean sendResult = true;
        
        // sendEmail returns an array of result objects.
        // Iterate through the list to inspect results. 
        // In this class, the methods send only one email, 
        // so we should have only one result.
        for (Messaging.SendEmailResult res : results) {
            if (res.isSuccess()) {
                System.debug('Email sent successfully');
            }
            else {
                sendResult = false;
                System.debug('The following errors occurred: ' + res.getErrors());                 
            }
        }
        
        return sendResult;
    }

}