Core/Email: Sent items didn't have BCC address header since v6.8

www/go/core/mail/PHPMailer.php

@@ -353,4 +353,32 @@ private function inlineTextExists(): bool
  return false;
  }
 
+ /**
+ * Returns the whole MIME message.
+ * Includes complete headers and body.
+ * Only valid post preSend().
+ *
+ * @see PHPMailer::preSend()
+ *
+ * @return string
+ */
+ public function getSentMIMEMessage()
+ {
+ $header = $this->MIMEHeader;
+
+ // PHPMailer leaves BCC out of headers when using SMTP. We want this header for our sent items
+ // source. So we append it here.
+ if (
+ (
+ 'sendmail' !== $this->Mailer && 'qmail' !== $this->Mailer && 'mail' !== $this->Mailer
+ )
+ && count($this->bcc) > 0
+ ) {
+ $header .= $this->addrAppend('Bcc', $this->bcc);
+ }
+
+ return static::stripTrailingWSP($header . $this->mailHeader) .
+ static::$LE . static::$LE . $this->MIMEBody;
+ }
+
 }