diff --git a/kallithea/lib/helpers.py b/kallithea/lib/helpers.py
--- a/kallithea/lib/helpers.py
+++ b/kallithea/lib/helpers.py
@@ -85,7 +85,7 @@ def html_escape(s):
         .replace(">", ">")
         .replace("<", "&lt;")
         .replace('"', "&quot;")
-        .replace("'", "&apos;")
+        .replace("'", "&#39;") # some mail readers use HTML 4 and doesn't support &apos;
         )
 
 def js(value):
diff --git a/kallithea/tests/models/test_dump_html_mails.ref.html b/kallithea/tests/models/test_dump_html_mails.ref.html
--- a/kallithea/tests/models/test_dump_html_mails.ref.html
+++ b/kallithea/tests/models/test_dump_html_mails.ref.html
@@ -94,7 +94,7 @@ View Comment: http://comment.org
     <tr>
         <td width="20px" style="width:20px"></td>
         <td>
-            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the new &apos;comment&apos;.<br/><br/> - and here it ends indented.</div></div>
+            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the new &#39;comment&#39;.<br/><br/> - and here it ends indented.</div></div>
         </td>
         <td width="20px" style="width:20px"></td>
     </tr>
@@ -253,7 +253,7 @@ View Comment: http://comment.org
     <tr>
         <td width="20px" style="width:20px"></td>
         <td>
-            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the new &apos;comment&apos;.<br/><br/> - and here it ends indented.</div></div>
+            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the new &#39;comment&#39;.<br/><br/> - and here it ends indented.</div></div>
         </td>
         <td width="20px" style="width:20px"></td>
     </tr>
@@ -430,7 +430,7 @@ View Comment: http://comment.org
     <tr>
         <td width="20px" style="width:20px"></td>
         <td>
-            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the new &apos;comment&apos;.<br/><br/> - and here it ends indented.</div></div>
+            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the new &#39;comment&#39;.<br/><br/> - and here it ends indented.</div></div>
         </td>
         <td width="20px" style="width:20px"></td>
     </tr>
@@ -607,7 +607,7 @@ View Comment: http://comment.org
     <tr>
         <td width="20px" style="width:20px"></td>
         <td>
-            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the new &apos;comment&apos;.<br/><br/> - and here it ends indented.</div></div>
+            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the new &#39;comment&#39;.<br/><br/> - and here it ends indented.</div></div>
         </td>
         <td width="20px" style="width:20px"></td>
     </tr>
@@ -728,7 +728,7 @@ Subject: Test Message
                     <td>
 <table cellpadding="0" cellspacing="0" border="0" width="100%">
     <tr>
-        <td style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the &apos;body&apos; of the &quot;test&quot; message<br/> - nothing interesting here except indentation.</div></td>
+        <td style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap"><div class="formatted-fixed">This is the &#39;body&#39; of the &quot;test&quot; message<br/> - nothing interesting here except indentation.</div></td>
     </tr>
 </table>
                     </td>
@@ -987,7 +987,7 @@ View Pull Request: http://pr.org/7
     <tr><td height="10px" style="height:10px"></td></tr>
     <tr>
         <td>
-            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap;color:#395fa0"><div class="formatted-fixed">This PR is &apos;awesome&apos; because it does &lt;stuff&gt;<br/> - please approve indented!</div></div>
+            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap;color:#395fa0"><div class="formatted-fixed">This PR is &#39;awesome&#39; because it does &lt;stuff&gt;<br/> - please approve indented!</div></div>
         </td>
     </tr>
     <tr><td height="15px" style="height:15px"></td></tr>
@@ -1162,7 +1162,7 @@ View Pull Request: http://pr.org/7
     <tr><td height="10px" style="height:10px"></td></tr>
     <tr>
         <td>
-            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap;color:#395fa0"><div class="formatted-fixed">This PR is &apos;awesome&apos; because it does &lt;stuff&gt;<br/> - please approve indented!</div></div>
+            <div style="font-family:Lucida Console,Consolas,Monaco,Inconsolata,Liberation Mono,monospace;white-space:pre-wrap;color:#395fa0"><div class="formatted-fixed">This PR is &#39;awesome&#39; because it does &lt;stuff&gt;<br/> - please approve indented!</div></div>
         </td>
     </tr>
     <tr><td height="15px" style="height:15px"></td></tr>