Insert,update,delete operation with Trigger context variables

Trigger AccountTrigger on Account(before insert,before update,before delete){
    //using trigger context variables

    if(Trigger.isInsert&&Trigger.isBefore){
        for(Account a:Trigger.new){
            a.Email__c='mbnchowdarysfdc@gmail.com';
        }
       
    }
    else if(Trigger.isUpdate&&Trigger.isBefore){
        for(Account a:Trigger.new){
            a.Email__c='mandalapubrahmanaidu1993@gmail.com';
        }
       
    }

    else{
        for(Account a:Trigger.old){
            a.addError('You cannot delete a record');
        }

       
    }
       
}