Strip quotes from html emails in PHP. See https://b-alidra.com/strip-quoted-text-from-html-emails/

strip_quotes_from_email.php

<?php
/**
 * Remove the quoted parts from the message body.
 *
 * It actually handles:
 * - Standard <blockquote>...</blockquote>
 * - Google
 * - Yahoo
 * - Thunderbird
 * - OSX Mail Client
 * - Roundcube
 *
 * @param Message $message
 *        The incoming or outcoming message to be cleaned
 *
 * @return Message
 *         The cleaned message
 */
public static function strip_quotes_from_message(Message $message)
{
    $els_to_remove = [
        'blockquote',                           // Standard quote block tag
        'div.moz-cite-prefix',                  // Thunderbird
        'div.gmail_extra', 'div.gmail_quote',   // Gmail

        'div.yahoo_quoted'                      // Yahoo
    ];

    $dom = new PHPHtmlParser\Dom;
    $dom->load($message->body);

    foreach ($els_to_remove as $el) {
        $founds = $dom->find($el)->toArray();
        foreach ($founds as $f) {
            $f->delete();
            unset($f);
        }
    }

    // Outlook doesn't respect
    // http://www.w3.org/TR/1998/NOTE-HTMLThreading-0105#Appendix%20B
    // We need to detect quoted replies "by hand"
    //
    // Example of Outlook quote:
    //
    // <div>
    //      <hr id="stopSpelling">
    //      Date: Fri. 20 May 2016 17:40:24 +0200<br>
    //      Subject: Votre facture Selon devis DEV201605201<br>
    //      From: [email protected]<br>
    //      To: [email protected]<br>
    //      Lorem ipsum dolor sit amet consectetur adipiscing...
    // </div>
    //
    // The idea is to delete #stopSpelling's parent...

    $hr  = $dom->find('#stopSpelling', /*nth result*/0);
    if (null !== $hr) {
        $hr->getParent()->delete();
    }

    // Roundcube adds a <p> with a sentence like this one, just
    // before the quote:
    // "Le 21-05-2016 02:25, AB Prog - Belkacem Alidra a écrit :"
    // Let's remove it
    $pattern = '/Le [0-9]{2}-[0-9]{2}-[0-9]{4} [0-9]{2}:[0-9]{2}, [^:]+ a &eacute;crit&nbsp;:/';
    $ps = $dom->find('p')->toArray();
    foreach ($ps as $p) {
        if (preg_match($pattern, $p->text())) {
            $p->delete();
            unset($p);
        }
    }

    // Let's remove empty tags like <p> </p>...
    $els = $dom->find('p,span,b,strong,div')->toArray();
    foreach ($els as $e) {
        $html = trim($e->innerHtml());
        if (empty($html) || $html == "&nbsp;") {
            $e->delete();
            unset($e);
        }
    }

    $message->body = $dom->root->innerHtml();

    return $message;
}
?>