Take stored email addresses from custom post type & turn into one string

Question

There are many ways you can do this. For my examples, I’m going to assume you’ve stored the emails in the post_title field. wp_mail takes a string or array in the to field, so you can do something like this…

<?php
$emails = get_posts(array(
    'post_type' => 'your_email_storing_type',
    'nopaging'  => true,
));

$to_send = array();

foreach ($emails as $e) {
    if (!e) {
        continue;
    }

    $to_send[] = $e->post_title;
}

wp_mail($to_send, /* ... */);

Or you can implode them all together (which you shouldn’t wp_mail will take care of it for you).

<?php
$emails = get_posts(array(
    'post_type' => 'your_email_storing_type',
    'nopaging'  => true,
));

$to_send = array();

foreach ($emails as $e) {
    if (!e) {
        continue;
    }

    $to_send[] = $e->post_title;
}

wp_mail(implode(',', $to_send), /* ... */);

Or you could go directly to wpdb and offload the concatenation to MySQL.

<?php
global $wpdb;

$emails = $wpdb->get_var("SELECT GROUP_CONCAT(post_title SEPARATOR ',') FROM {$wpdb->posts} WHERE post_title="your_email_storing_type"");

wp_mail($emails, /* ... */);