CREATE TABLE `virtual_users` (
  `id` int(11) NOT NULL auto_increment,
  `domain_id` int(11) NOT NULL,
  `password` varchar(106) NOT NULL,
  `email` varchar(100) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `email` (`email`),
  FOREIGN KEY (domain_id) REFERENCES virtual_domains(id) ON DELETE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

INSERT INTO `mailserver`.`virtual_users`
  (`id`, `domain_id`, `password` , `email`)
VALUES
  ('1', '1', ENCRYPT('firstpassword', CONCAT('$6$', SUBSTRING(SHA(RAND()), -16))), 'email1@example.com'),
  ('2', '1', ENCRYPT('secondpassword', CONCAT('$6$', SUBSTRING(SHA(RAND()), -16))), 'email2@example.com');

1. A random number is generated
2. A SHA1 hash is created from it
3. The SUBSTRING function throws away the first 16 characters and keeps the rest of the hash string
4. The remaining characters in the hash string are appended to the literal string '$6$'
5. That combined value is used as the salt for the ENCRYPT function
6. The resulting value is stored in the password field.

• https://library.linode.com/email/postfix/postfix2.9.6-dovecot2.0.19-mysql#sph_adding-data
• http://stackoverflow.com/questions/24186158/sha512-crypt-mysql-and-dovecot
• http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function_substring
• http://dev.mysql.com/doc/refman/5.5/en/encryption-functions.html#function_encrypt
• http://dev.mysql.com/doc/refman/5.5/en/encryption-functions.html#function_sha1
• http://stackoverflow.com/questions/24186158/sha512-crypt-mysql-and-dovecot
• http://stackoverflow.com/questions/16485906/mysql-encrypt-password-but-how-to-decrypt-it/16485963#16485963

<?php

$password = 'password';
$salt = 'salt';

$hash = hash('sha512', $salt.$password);

echo strlen($hash); // OUTPUTS 128

?>