I've gotten two reports of Outlook freezing since changing the structure of an email I send to use image sources like:


instead of:


Is this possible or is it a coincidence (2 reports out of 150k emails - but we've never had this reported before the change)?

  • Perhaps Outlook is treating them as UNC paths rather than URLs and freezing during the unsuccessful attempt to access the host as a file server?
    – Kevin Reid
    Apr 15, 2011 at 0:02
  • I've confirmed that this will freeze most versions of Outlook. I'm amazed that hackers aren't exploiting this. May 19, 2011 at 22:36

2 Answers 2


I've had problems with links like this in Outlook when Internet Explorer is not the default browser. In my case the user had Chrome as the default browser and Outlook was hanging handing over the link to Chrome - it did eventually load the image, but it would take literally 5 minutes of being non-responsive.

Anyway, I would have thought that you really should be specifying the protocol in the hyperlink as best practice, but I'm not sure it will make much difference in this case

  • To be clear, these are attributes in the image tag like this, not hrefs: <img src="//example.com/file.jpg" /> Apr 14, 2011 at 20:47
  • 1
    Can you believe it: nothing has really changed since early 2011 (as of end of 2015)! I stumbled upon it in my work. No. Outlook still doesn't support protocol relative links. Whereas 'best practices' Jon Reeves talked about would be to use them rather than not. Nov 6, 2015 at 11:08

This is a known bug in Outlook 2010 (see here a Microsoft rep recognizes this). You can download the hotfix (that only took them 2 years to publish :-) ) here.

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