Whenever a client of mine sends out attachments they keep turning into winmail.dat files. However, if I send one to my exchange account or gmail they seem fine. However, if they send to their e-mail which is an internet account@isp.tld they get the winmail.dat instead of an attachment.

The emails go out as HTML as I have seen in the settings and the profile was recreated to remove all possible culprits so that they operate at default settings.

Here is the view-source of the email. It looks like it is in HTML: (viewing from outlook 2013 on my end at one of their emails)

<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">


><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />

Other ideas on how to debug this issue?


I have run into this issue before it is because the emails are sending as rich text documents.


Here is a kb that can hopefully help you out.

  • I figured this was the cause but everything under Outlook2013 options shows sending as HTML. I have a client here works fine default settings. I reset theirs to a new profile and they seem to still have the same issues. Is there another possible fix or a hidden setting to force HTML? We also use OFFICE365 I think it is for our exchange emails – Jason Jun 3 '15 at 14:50
  • The first post is all the familiarity I have with the issue, however if you are familiar with Powershell I would recommend trying this support.microsoft.com/en-us/kb/2487954/en-us – Daniel Hayes Jun 3 '15 at 15:10

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