Fastest way to delete matching rows in MySQL?

Question

I have more than 10 million records in a table. I want to delete the records where the email column contains .ac..

What is the fastest method to perform the task?

Table Schema

CREATE TABLE `master` (
   `id` int(11) NOT NULL AUTO_INCREMENT,  
   `email` varchar(255) NOT NULL,
   PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=1 DEFAULT CHARSET=latin1;

Delete Query

DELETE FROM `master` WHERE ( email LIKE "%.ac.%" );