I can see that Zimbra 5.x and 6.x (6.0.4) does not produce valid html code for outgoing emails.
Why?
My Thunderbird make sure it's always valid xhtml code that I can verify on
The W3C Markup Validation Service.
Here is a html mail I sent with the only word "test" in it:
Code:
<html>
<head>
<style type='text/css'>
p { margin: 0; }
</style>
</head>
<body>
<div style='font-family: Verdana, Arial, Helvetica, sans-serif; font-size:12pt; color: #000000'>
test<br>
</div>
</body>
</html> The only things missing in this simple code above, is
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> and a title in the head, like
<title>subject</title>. After this, it will validate as html 4.01.
So why ain't Zimbra producing code that follows a standard? It must be a reason for choosing to do like this?
Bugzilla
Wiki
Source
Why not valid html code in outgoing emails? 
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