The mystery of the missing e-mail attachments

We have had a few people contact us asking if our e-mail filtering system "strips" attachments. The short answer to this is NO. If we don't like the attachment we block/reject the entire e-mail. Having said this people are still receiving e-mail that appear to have no attachments. If, however, you look at the size of the e-mail it is evident that it's not just a few lines of text.

This issue is caused by Microsoft Outlook!

If you get a query like this, ask the person to open up said e-mail, click on File | Attachments | View Attachments. This opens a different view of the e-mail and the attachments can be seen there.

Here are the details on the Outlook issue:

Thanks to the folk at Quarelle (

A common problem when using Microsoft Outlook is to send an email with an attachment to someone using Microsoft Outlook Express [or GroupWise] and find that they claim there is no attachment. If you look at the size of the received email you will usually see it is rather large for just a text email, the attachment is actually there, you just can't see it!

This is caused by the WINMAIL.DAT file format it uses.

If you have Outlook set to send messages using RTF format, then any attachments you send will be combined into a file called WINMAIL.DAT which is attached to the email. RTF is, in theory, a "standard" format, but each application which uses it seems to use a different version of this standard. In fact, the only software which understands these WINMAIL.DAT files is Microsoft Outlook.

Attachments sent in WINMAIL.DAT format will be unusable to those who do not use Outlook - even Outlook Express (as supplied free with Internet Explorer) does not understand these files. Even worse, the way that the attachment is added to the email means that many email packages will not even show that there is an attachment present. If you have ever been told by someone that an attachment was missing from an email you sent, then this may be why!

It is our strong recommendation that you disable the use of RTF within Outlook. To do this, in Outlook select Tools -> Options -> Mail Format. If the current selection under Message Format is "Microsoft Outlook Rich Text" then change it; we would suggest either "Plain Text" or "HTML". Different versions of Outlook (and different configurations) have different options and in different places.


How To-Best Practice
Comment List
  • If you're missing some attachments or whole emails, then this article will teach you how to recover deleted emails in outlook. Hope you won't face this issue anymore. 

  • how to stop the winmail.dat attachment from exchange 2003?
  • would this also cause problems with mail coming in that has no attachments? I am having issues with emails coming in, with no body. BUT, when I go to File/View/Attachments, the body of the message shows up in the mime.822 header file. Even choosing View Text or View Html will not display the body of the message. Any help would be appreciated!!!

    cmcneill @ nhrmc dot org
  • Before our company was acquired, we were a Netware/GroupWise/ZENworks/BorderManager operation (I miss those days.)

    The winmail.dat issue has been happening to us between different Outlook 2003 users on the same Exchange 2003 cluster. So having Outlook on the receiving end is no guarantee that the attachments will appear correctly.

    Having the sender change to HTML mode doesn't stop it either. Text mode helps but I'm not yet convinced that it completely eliminates the problem.

    Microsoft recommended that we upgrade (replace) our '03 cluster with '07 running on Server 2008. So we just finished that, and I haven't yet heard any reports of the winmail.dat problem since then.

    GroupWise rocks. I wish we could still run it.

    - Kevin