From 2b8eb74b7a5d6ecd6ce3601b2cc98847255c80fc Mon Sep 17 00:00:00 2001
From: Tony Murray <murraytony@gmail.com>
Date: Mon, 9 Aug 2021 09:17:32 -0500
Subject: [PATCH] Detect sending non-html emails as html (#13114)

* Detect sending non-html emails as html
and use <br /> for line returns instead of \r\n

* Fix style
---
 LibreNMS/Alert/Transport/Mail.php | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/LibreNMS/Alert/Transport/Mail.php b/LibreNMS/Alert/Transport/Mail.php
index 5b3edafb1c..2628bb56a5 100644
--- a/LibreNMS/Alert/Transport/Mail.php
+++ b/LibreNMS/Alert/Transport/Mail.php
@@ -35,9 +35,17 @@ class Mail extends Transport
     public function contactMail($obj)
     {
         $email = $this->config['email'] ?? $obj['contacts'];
-        $msg = preg_replace("/(?<!\r)\n/", "\r\n", $obj['msg']); // fix line returns for windows mail clients
+        $html = Config::get('email_html');
 
-        return send_mail($email, $obj['title'], $msg, (Config::get('email_html') == 'true') ? true : false);
+        if ($html && ! $this->isHtmlContent($obj['msg'])) {
+            // if there are no html tags in the content, but we are sending an html email, use br for line returns instead
+            $msg = preg_replace("/\r?\n/", "<br />\n", $obj['msg']);
+        } else {
+            // fix line returns for windows mail clients
+            $msg = preg_replace("/(?<!\r)\n/", "\r\n", $obj['msg']);
+        }
+
+        return send_mail($email, $obj['title'], $msg, $html);
     }
 
     public static function configTemplate()
@@ -56,4 +64,9 @@ class Mail extends Transport
             ],
         ];
     }
+
+    private function isHtmlContent($content): bool
+    {
+        return $content !== strip_tags($content);
+    }
 }