Fix single underscores in email templates

provides a better fix for #1800

CHANGELOG.md

@@ -7,6 +7,7 @@
 
 ### Fixed
 - Fixed a bug where entry version data was not including newly-created Matrix block IDs, so they would be re-created from scratch when loading the version. ([#2498](https://github.com/craftcms/cms/issues/2498))
+- Fixed an error that could occur if an email template included any Twig filters with a single underscore.
 
 ## 2.6.3010 - 2018-02-21
 

src/services/EmailService.php

@@ -438,11 +438,17 @@ private function _sendEmail(UserModel $user, EmailModel $emailModel, $variables
 				}
 				else
 				{
-					// TODO: This won't be necessary in 3.0 thanks to Parsedown
-					$emailModel->body = preg_replace('/(?<=[a-zA-Z])_(?=[a-zA-Z])/', '\_', $emailModel->body);
-
 					// They didn't provide an htmlBody, so markdown the body.
-					$renderedHtmlBody = craft()->templates->renderString(StringHelper::parseMarkdown($emailModel->body), $variables);
+
+					// Don't parse _text_ as italics because https://github.com/craftcms/cms/issues/1800
+					if (!class_exists('\Markdown_Parser', false))
+					{
+						require_once craft()->path->getFrameworkPath().'vendors/markdown/markdown.php';
+					}
+					$md = new \Markdown_Parser();
+					unset($md->em_relist['_']);
+
+					$renderedHtmlBody = craft()->templates->renderString($md->transform($emailModel->body), $variables);
 					$email->msgHTML($renderedHtmlBody);
 				}