If you or your recipients receive a winmail.dat attachment inside a secure email, there is a misconfiguration on the sender's side, either in Microsoft Outlook or Exchange.

Solution at the Sender's Microsoft Outlook Level

There are a few different options to check on Microsoft Outlook to ensure emails are being sent via HTML and not Rich Text Format (RTF).

Check the Formatting of All Emails - Version 1

Check the formatting of all emails by following the steps below:

1. Navigate to File Options.
2. Select Mail.
3. Ensure the Compose messages in this format option is set to HTML.

Check the Formatting of All Emails - Version 2

Check the formatting of a new email or the formatting of a reply to an email. You can check this by selecting Format Text from the top bar on a new email or reply and ensuring that HTML is selected.

Check the Formatting of All Emails - Version 3

Check the formatting settings on a per-user basis, as there may be different settings. To do this, follow the steps below:

1. Select the People button at the bottom left-hand corner of Microsoft Outlook.
2. Double-click the user's email address to which you are having problems sending. This action will open their contact card.
3. Right-click their email address on this contact card and select Open Outlook Properties.
4. On the new window that appears, ensure emails are not being sent in Rich Text Format.

Delete the Cache of the Recipient's Email Address

The cached version of the recipient's email address may cause issues. To delete the cached version of a recipient's email address, follow the steps below:

1. On a new email, start typing the recipient's email address in the To field.
2. The drop-down menu of cached email addresses will be displayed. Select the X icon after the recipient.
3. Type the recipient's email address again manually. This action should resolve the issue.

Solution at the Sender's Server Level

When our gateway receives an email from Microsoft Exchange, it wraps everything up in a .switch file, and occasionally, a Winmail.dat attachment is included. Unfortunately, in certain instances, Microsoft Exchange may not be able to process the email correctly before passing it on to Gateway.

The attachment seems lost before we process the message for encryption. This issue could be a variety of reasons, such as:

1. We encourage you to consider whether these senders are using RTF instead of the default HTML formatting. This action can be done on a per-recipient basis.
2. Changing an attribute in the actual contact on the Global Address List may resolve the issue.

Microsoft Exchange 2007/2010

To change an attribute in Microsoft Exchange 2007/2010, follow the steps below:

1. Run the Exchange System Manager program.
2. In the left panel, navigate to Global Settings Internet Message Formats Standard.
3. In the context menu, choose Properties and navigate to the Advanced tab.
4. Set the Exchange rich-text format option to Never use.

Microsoft Exchange 2013

To change an attribute in Microsoft Exchange 2013, follow the steps below:

1. Open Exchange Management Shell.

2. To see your current settings, run the following command:

   Get-RemoteDomain | Where {$_.TNEFEnabled -ne $false}

3. For each Remote domain, run the following command:

   Set-RemoteDomain -Identity DomainName -TNEFEnabled $false