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Chris MillardFlag for United Kingdom of Great Britain and Northern Ireland

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Winmail.dat for just one recipient

A customer has two offices - one in the UK, one in Australia. They share a common TLD for their email. All inbound email passes through the cloud based FuseMail filtering service, and FuseMail forward emails to either the UK or Australian Exchange servers based on group membership.

When users in Australia send an email to a specific user in the UK, the UK users gets any embedded images or attachments as a winmail.dat attachment. If other UK users are CC'd into the same email, then those recipients see the images in the email and have the correct attachments, but this one user still has just a winmail.dat attachment. And it is ONLY when receiving emails from the Australian users.

On the UK Exchange server, the customer is also using Exclaimer for adding signatures and disclaimers to emails.

I cannot figure out WHAT is causing this one recipient to keep getting the attachments as winmail.dat.

Just to add to this, it doesn't matter if this one user uses Outlook (in cached mode), OWA, his tablet or iPhone - in all cases, when he gets emails from the Australian users, he always ends up with winmail.dat attachments (even when other recipients do not).
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Muzafar Momin
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Recipients notify you that the e-mail message you sent appears to them as a message with an attachment called winmail.dat.


You are using the Rich Text message format, which the recipient's e-mail program cannot interpret correctly.


Send your messages in either HTML or plain text format.

Send messages in HTML or plain text format

On the Tools menu, click Options, and then click Mail Format.

Under Message Format, in the Compose in this message format list, click HTML or Plain Text.

Click OK.

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That's not the case. The Exchange server in Australia has been set to NOT allow RTF emails.  We have also ensured that they are sending using HTML.
in that case can you check for any virus or malware in users system as well as on Australia exchange server
The recipient that they are sending to, do they use the same filtering service (not clear if the recipient is internal to the company or not)?

If they do, does the filtering service allow per user policies or configuration settings and have you checked these settings?

Is the sender using Outlook?

Have you tried using another mail client to send messages through the Exchange server to the recipient?

Are there any additional spam filters (local antivirus or otherwise) that could be at play here?

Check out this support ticket with Microsoft, that includes a resolution. See if that helps.
Hi Katherine,

Unfortunately, these are the same steps that have already been provided by Muzafar previously.  To which the author has already stated that it is not an RTF issue.

Saige - Should have reloaded the page before posting. :)
Just to confirm. I have a test account on the same UK server. I had a user in Australia send a new email with attachment to both myself AND to the affected user.

I get the attachment in its original form, whereas the affected user is getting this as the winmail.dat attachment.

It is not device specific - it happens whether he opens the email in Outlook, OWA or on his iPhone.

Having checked the logs on the filtering service, it is not a winmail.dat attachment when it passes through there, so it appears to be an Exchange 2010 issue at the UK end.
I've just looked a bit more into this, and it appears that the recipient with the problem, is receiving the messages in plain text format whereas everyone else is getting them in HTML, so I need to see where this is happening.
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Chris Millard
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The sending server had a CONTACT for the UK user who was receiving the winmail.dat. The contact has now been removed, and the UK recipient is now receiving emails in the correct format and without a winmail.dat attachment.