Get email domain from a user’s email

// Verbose example to show steps:
$user_email   = "example@domain.com";
$email_array  = explode( "@", $user_email );
$email_domain = array_pop( $email_array );
echo $email_domain; // Will output "domain.com"


// Simple one line, get domain from email:
$domain = array_pop( explode( "@", $user_email ) );


/**
 * Here's a more detailed example of getting a user's email 
 * and then extracting the domain in WordPress. (assumes 
 * you have the user ID in $user_id).
 * 
 * @uses get_user_by()
 */
$user = get_user_by( 'ID', $user_id );
$user_email = $user->user_email;
$domain = array_pop( explode( "@", $user_email ) );


/**
 * Similar WP example to handle getting the email domain
 * when the user registers (assumes default WP reg form).
 */
 $user_email = sanitize_email( $_POST['user_email'] );
 $domain = array_pop( explode( "@", $user_email ) );