<apex:page Controller="emailclass">
<apex:form >
<apex:commandButton value="sendmail" action="{!sendemail}"/>
</apex:form>
</apex:page>

public with sharing class emailclass {
public list<id> contactids;
public emailclass(){
list<contact> con=[select id from contact limit 10];
for(integer i=0;i<10;i++)
{
contactids.add(con[i].id);
}
}
  public PageReference sendemail() {
    Messaging.MassEmailMessage mail=new Messaging.MassEmailMessage();
    mail.settargetobjectids(contactids);
    Message.sendemail(new Messaging.MassEmailMessage[]{mail});
 
        return null;
        }
        

}