[BUGFIX] Fix the preview mail sending

Classes/Service/MailTemplateService.php

@@ -651,14 +651,18 @@ class MailTemplateService {
 		$emailBody = nl2br($emailBody);
 		$emailBody = preg_replace('/(<br[\s]?[\/]?>[\s]*){3,}/', '<br><br>', $emailBody);
 
-		if (!$isPreview) {
-			$mail = $this->addMailToMailQueue(
-				$this->extensionKey, $this->templateName, $subject, $emailBody, $this->priority,
-				0, 0, $this->language, $siteRootId
-			);
-			if ($this->ignoreMailQueue) {
-				$success = $this->sendMailFromQueue($mail->getUid());
-			}
+		$mail = $this->addMailToMailQueue(
+			$this->extensionKey, $this->templateName, $subject, $emailBody, $this->priority,
+			0, 0, $this->language, $siteRootId
+		);
+		if ($this->ignoreMailQueue) {
+			$success = $this->sendMailFromQueue($mail->getUid());
+		}
+
+		if ($isPreview) {
+			$mailRepository = $this->objectManager->get(MailRepository::class);
+			$mailRepository->remove($mail);
+			$this->persistenceManager->persistAll();
 		}
 
 		return $success;