Strips out all characters that are not allowable in an email.

function sanitize_email( $email ) {
	// Test for the minimum length the email can be.
	if ( strlen( $email )  count( $subs ) ) {
		/** This filter is documented in wp-includes/formatting.php */
		return apply_filters( 'sanitize_email', '', $email, 'domain_no_periods' );
	}

	// Create an array that will contain valid subs.
	$new_subs = array();

	// Loop through each sub.
	foreach ( $subs as $sub ) {
		// Test for leading and trailing hyphens.
		$sub = trim( $sub, " tnrx0B-" );

		// Test for invalid characters.
		$sub = preg_replace( '/[^a-z0-9-]+/i', '', $sub );

		// If there's anything left, add it to the valid subs.
		if ( '' !== $sub ) {
			$new_subs[] = $sub;
		}
	}

	// If there aren't 2 or more valid subs.
	if ( 2 > count( $new_subs ) ) {
		/** This filter is documented in wp-includes/formatting.php */
		return apply_filters( 'sanitize_email', '', $email, 'domain_no_valid_subs' );
	}

	// Join valid subs into the new domain.
	$domain = implode( '.', $new_subs );

	// Put the email back together.
	$sanitized_email = $local . '@' . $domain;

	// Congratulations, your email made it!
	/** This filter is documented in wp-includes/formatting.php */
	return apply_filters( 'sanitize_email', $sanitized_email, $email, null );
}