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Dreaded Winmail.DAT

Kidamazon1 asked
Hi Guys,

I have a problem with users (externally) on Apple (crappy Mail) Client receiving Winmail.dat attachments from my domain. I fully understand that this is a TNEF issue with e-mail clients that are not on Microsoft Exchange (backend) or on Outlook (front ends). So please don't treat this question or prescribe the usual Microsoft KB article as a solution because I've tried that and it has not worked thus far.  

Just fyi:
Here is are my backend specs: Exchange 2010 with all of my users sending emails are on either Outlook 2010 or Outlook 2011 for Macs.

Now, one of my external clients having the issue with my domain sent attachments has given me access by creating me an account on their system which is a generic hosting company using POP and IMAP to relay the emails along to Apple Mail client. I've requested this account to test sending attachment with from my domain to theirs.

During my testing I've tried the numerous recommendations by Microsoft and others here in this forum to no avail. But here is the question that I cannot answer.

For some odd reason that I am not able to explain yet the new account created for me does not exhibit the problem and attachments reach my account on that system correctly but another person (who created the account for me) has issue with my email address and receiving the Winmail.DAT attachments when I sent him the emails.

This person advised me that at first when he started receiving emails from my domain there were no issues with attachments and that it begun happening after a while but the problem has not changed since it begun happening.

If the issue was really my Outlook client then it would be as simple as sending HTML or Plain Text emails and the problem would be solved. Furthermore, my new account on that system has not had any problems with the test attachments that I am sending but my colleagues account is,  both his apple mail and iphone are showing Winmail.DAT when sending emails.

Should I look into my Exchange server settings? What should my next steps be?

Please note: The I've also turned off any SPAM filtering used at the clients end to ensure that it is not an issue.

Please help,

Confused IT Manager :-)
Watch Question

Some primer questions:

1.  With regards to the test account on the clients side, how are you accessing this account?
2.  Do you or the client have an intermediary (spam filter or otherwise)?  If so, is your test account's email being passed through these intermediaries?
3.  What does happen when you send an email from your Outlook client: as plain text? as html?
4.  Can you provide the host headers of a test message (removing any sensitive information)?


Do you have these clients saved in your address book?  If so:
1. Open his/her contact
2. Double-click on his email address and choose Outlook Properties from the options button
3. In the Internet Format field, change the value to Send Plain Text only

This has worked for us.


Hi IT_Saige,

Here are the answers below:

1. I am accessing the test account on Apple Mail on a Macbook running the latest OS X 10.10
2. There is a SPAM filter applied by default but I've made sure that the guy who receives my Winmail.dat attachments has this turned of for his account and on my own test account.  
3. HTML and Plain Text formatted email results in the same problem to the one user who alert me of the issue. However, on my test account it shows the normal attachments as they are supposed to be.
4. I am uncertain on how to get the email header information on Apple Mail but I can provide those as soon as I figure that out.

For question 2, I assume then, that you do not have any outbound filtering and/or smart hosting on your side?



Hi M Patton,

Thanks but that is something I have tried and is one of the Microsoft suggested solutions when dealing with this issue. I only wished this would have been this super easy.

Again, I appreciate your help but I need more than the basics here as the problem seems to be more persistent in my case.


Confused IT Manager



I do have a SPAM filtering on my end. Should I whitelist that domain for sending?


I would definitely start there.  This problem can be caused by intermediaries (such as spam filters).




I will try this but it doesn't really explain why my test account does not have the issue but the other account does.

Let me get the headers to see if I could get anything from them.

That does perplex me, although, many spam filters have exceptions...  Is it possible that you have their current addresses on an exception list somewhere in the spam filtering software (on both sides of the equation).