We have a tracking pixel in one of our emails and our the most frequent user agent is this strange one:

Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C; .NET4.0E)

If you enter this into user-agent.info you will see that it claims to be Windows 7 (Windows NT 6.1) but at the same time IE 7, which isn't available for this OS version.

Since this is an email I'm guessing that it could be some Microsoft email program (Windows Mail, Outlook Express?) that is embedding an IE7 engine.

Does anyone know more?

PS: I'm aware that user agents are easily spoofed but that would have to be a pretty determined troll.

1 Answer 1


It could be IE9 running in IE7 compatibility view, although I can't imagine that being "the most frequent user agent".

Like you say, this is most probably a (Windows) email client. Email clients are quite archaic in their rendering abilities, so IE7 is no surprise - in fact I thought later versions of Office (2007+) went further backwards and used the rendering engine from Word?

The first part would seem to be consistent with Outlook 2007, Outlook 2010 and Outlook 2013. However, these user agents usually identify themselves as being "MSOffice" or "Microsoft Outlook" respectively.

Outlook Express / Windows Live Mail would seem to identify themselves as "Outlook-Express".

However, this question (unanswered) on StackOverflow is asking the question of how to tell the difference between Outlook 2003 (and earlier) and a regular IE browser - since the two look very similar.

My best guess therefore is that your user agent string is from Outlook 2003 (which I imagine is still a popular version). However, the niggling problem with this is that MSIE 7 only first appeared around 2005/6. It's hard to imagine that Microsoft would have looked ahead this far! If it is Outlook 2003 then I can only assume that various updates (perhaps to IE/Trident) will have updated the UA string also?

  • 1
    You are right. I ran a test in Litmus and found out that Outlook 2003 indeed identifies itself as IE7. Commented Feb 12, 2014 at 15:13

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