SingleEmailMessage Vs MassEmailMessage | Send Email by Apex

SingleEmailMessage Vs MassEmailMessage

	SINGLE EMAIL	MASS EMAIL
Multiple recipients?	Yes	Yes
Personalized body?	Yes (single body only)	Yes
Special permission needed?	No	Yes, has to be enabled
Merge fields?	Yes	Yes
Personalized merge fields?	Yes (only one record at a time)	Yes
Templates?	Yes	Yes
Template possibilities?	Text/HTML/Visualforce/Custom Templates	Text/HTML/Custom Template

SingleEmailMessage:

Single emails are like regular individual emails that may go to one or more addresses (to/cc/bcc), but each of these emails has the same body

Messaging.SingleEmailMessage message = new Messaging.SingleEmailMessage();
message.toAddresses = new String[] { 'abc@gmail.com', 'xyz@gmail.com' };
message.optOutPolicy = 'FILTER';
message.subject = 'Opt Out Test Message';
message.plainTextBody = 'This is the message body.';
Messaging.SingleEmailMessage[] messages =   new List<Messaging.SingleEmailMessage> {message};
Messaging.SendEmailResult[] results = Messaging.sendEmail(messages);

if (results[0].success) 
{
    System.debug('The email was sent successfully.');
} else 
{
    System.debug('The email failed to send: ' + results[0].errors[0].message);
}

Please check below post to see all other method
https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_classes_email_outbound_single.htm 

 
MassEmailMessage:

Mass emails typically go to a large number of addresses (currently capped to 250 per email), with personalized message bodies.

public void SendEmail()
{
 List<contact> lstcon=[Select id from contact limit 2];
 List<Id> lstids= new List<Id>();
 for(Contact c:lstcon)
 {
  lstids.add(c.id);
 }
 EmailTemplate et=[Select id from EmailTemplate where name = 'EmailTemplatename' limit 1];
 
 Messaging.MassEmailMessage mail = new Messaging.MassEmailMessage();
 mail.setTargetObjectIds(lstIds);
 mail.setSenderDisplayName('System Admin');
 mail.setTemplateId(et.id);
 Messaging.sendEmail(new Messaging.MassEmailMessage[] { mail });
}

 Please check below post to see all other method

https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_classes_email_outbound_mass.htm 

  
Related link
https://developer.salesforce.com/page/An_Introduction_To_Email_Services_on_Force.com