Disable wp_mail, and save to file only

wp_mail_disable.php

<?php 
/**
 * WP Mail for the development site, should not be used on production site
 * 
 * Throw this in to your *wp_config.php*
 */
function wp_mail($to, $subject, $message, $headers = '', $attachments = array() ) {
	$emails_dir = __DIR__ . "/.emails/";
	if (!file_exists($emails_dir)) {
		mkdir($emails_dir);
	}
	$email = json_encode(array(
		"to" => $to,
		"subject" => $subject,
		"message" => $message,
		"headers" => $headers,
		"attachments_count" => count($attachments),
		"trace" => debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS),
	), JSON_PRETTY_PRINT);
	file_put_contents($emails_dir . date("Y-m-d\\THis") . "_" . uniqid() . ".json", $email);
	return true;
}

xxx_index.php

<?php 
// Place this to the .emails directory, should not be used on production site


if (isset($_GET["email"])) {
    $filename = preg_replace("/[^a-zA-Z0-9-\._]+/", "", $_GET["email"]);
    $json = json_decode(file_get_contents($filename), true);
    if (!$json) {
        return;
    }
    ?>
    <?php foreach ($json as $key=>$value): ?>
    <article>
        <h2><?php echo $key; ?></h2>
        <?php 
        if (is_string($value) && strpos($value, "<") === 0) {
            ?>
            <a href="#" id="show_html">Show HTML in iframe</a><br><br>
            <script>
                var EMAIL_HTML = <?php echo json_encode($value); ?>;
                var LINK = document.querySelector("#show_html");
                LINK.addEventListener("click", function (e) {
                    var iframe = document.createElement("IFRAME");
                    iframe.setAttribute("sandbox", "");
                    iframe.style.width = "100%";
                    iframe.style.height = "700px";
                    iframe.setAttribute("srcdoc", EMAIL_HTML);
                    LINK.parentNode.insertBefore(iframe, LINK);
                    LINK.parentNode.removeChild(LINK);
                    e.preventDefault();
                })
            </script>
            <div>
                <?php echo preg_replace(
                    "/\s+/", " ", strip_tags($value)
                );?>
            </div>
            <?php 
            
        } else if (is_string($value)) {
            echo nl2br(htmlentities($value));
        } else {
            echo '<pre>';
            echo strip_tags(print_r($value, true));
            echo '</pre>';
        }
        ?>
    </article>
    <?php endforeach; ?>
    <?php 
    return;
}

?>
<style>
    body {
        font-family: "San Francisco", "Segoe UI", sans-serif;
    }
    table {
        width: 100%;
        table-layout: fixed;
    }
    table th {
        text-align: left;
    }
    table td {
        padding: 0.6em 0.2em;
        vertical-align: top;
    }
    .date {
        width: 4em;
    }
    .time {
        width: 4em;
    }
    .to {
        width: 12em;
        text-overflow: ellipsis;
        overflow: hidden;
    }
    .debug {
        width: 4em;
    }
    .attachments {
        width: 4em;
    }
    .email {
        width: 100%;
    }
    pre {
        font-family: "Fira Code", monospace;
        font-size: 12px;
    }
    iframe {
        border: 1px solid black;
    }
</style>
<table>
    <tr>
        <th class="date">Date</th>
        <th class="time"></th>
        <th class="to">To</th>
        <th class="subject">Subject</th>
        <th class="attachments">Attach</th>
        <th class="debug"></th>
    </tr>
<?php 
$emails = array_reverse(glob("*.json"));
foreach ($emails as $email) {
    $json = json_decode(file_get_contents($email), true);
    if (!$json) {
        continue;
    }
    $date = filemtime($email);
    $to = $json["to"];
    $message = $json["message"];
    $subject = $json["subject"];
    $uid = uniqid();
    $trace = $json["trace"];
    $headers = $json["headers"];
    $attachments_count = $json["attachments_count"];
    ?>
    <tr>
        <td class="date"><?php echo date("j.n.Y", $date); ?></td>
        <td class="time"><?php echo date("H:i:s", $date); ?></td>
        <td class="to"><?php echo htmlentities($to); ?></td>
        <td class="email">
            <a id="emaillink<?php echo $uid; ?>" href="#"><?php echo htmlentities($subject); ?></a>

            <script>
                (function () {
                    let LINK = document.querySelector("#emaillink<?php echo $uid; ?>");
                    LINK.addEventListener("click", function (e) {
                        let EMAIL_SHOW = document.querySelector("#emailshow<?php echo $uid; ?>");
                        let EMAIL_HTML = document.querySelector("#email<?php echo $uid; ?>");
                        
                        if (EMAIL_SHOW.style.display == "block") {
                            EMAIL_SHOW.style.display = "none";
                        } else {
                            EMAIL_SHOW.style.display = "block";
                        }
                        EMAIL_SHOW.setAttribute("srcdoc", EMAIL_HTML.textContent);
                        // LINK.parentNode.insertBefore(iframe, LINK);
                        // LINK.parentNode.removeChild(LINK);
                        e.preventDefault();
                    })
                })();
            </script>
        </td>
        <td class="attachments">
            <?php echo htmlentities($attachments_count); ?>
        </td>
        <td class="debug">
            <a id="debuglink<?php echo $uid; ?>" href="#">Debug</a>

            <script>
                (function () {
                    let LINK = document.querySelector("#debuglink<?php echo $uid; ?>");
                    LINK.addEventListener("click", function (e) {
                        let DEBUG_HTML = document.querySelector("#debug<?php echo $uid; ?>");
                        if (DEBUG_HTML.style.display == "block") {
                            DEBUG_HTML.style.display = "none";
                        } else {
                            DEBUG_HTML.style.display = "block";
                        }
                        e.preventDefault();
                    })
                })();
            </script>

        </td>
    </tr>
    <tr>
        <td colspan="6">
            <div id="email<?php echo $uid; ?>" style="display: none">
                <?php echo htmlentities($message); ?>
            </div>
            <iframe id="emailshow<?php echo $uid; ?>" style="display: none; width: 100%; height: 700px;"></iframe>
            <pre id="debug<?php echo $uid; ?>" style="display: none; width: 100%; overflow: scroll;"><?php print_r($headers); ?><?php print_r($trace); ?></pre>
            
        </td>
    </tr>
    <?php 
} ?>

</table>