I had an array of email addresses ($email_addresses) in WordPress (PHP).

The best practice is, of course, to sanitize all addresses. This can be done easily using the built-in sanitization function in WordPress: sanitize_email.

The old method would be to use foreach and sanitize each email address separately. For example:

$sanitized_email_addresses = array();

foreach ( $email_addresses as $email_address ) {
	$sanitized_email_addresses[] = sanitize_email( $email_address );

However, this can be done with only one line using array_map:

// Sanitize all email addresses.
$email_addresses = array_map( 'sanitize_email', $email_addresses );

This will run the sanitize_email function for each of the values in the array.

We could, of course, use any other sanitization function as needed (for instance, sanitize_text_field for an array of text inputs).