If you or your recipients are receiving a winmail.dat attachment inside a secure email, there will be a misconfiguration on the sender's side, either in Outlook or their Exchange. 

Resolving at the Senders Outlook Level

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

Suggestion 1

Checking the formatting of all emails by:

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

Suggestion 2

Deleting the cached version of the recipients email address which may be causing issues. To delete the cached version of a recipients email address you need to:

  1. On a new email, start typing the recipients email address in the To field
  2. The drop down of cached email addresses will show, select 'X' after the recipients one.
  3. Type the recipients email address again manually and this should resolve the issue.

Suggestion 3

Checking the formatting of emails on a new email, or a reply to an email. You can check this by selecting 'Format Text' from the top bar on a new email/reply and ensuring 'HMTL' is selected.

Suggestion 4

Checking the formatting settings on a per-user basis as there may be different settings. To do this

1. Selecting the 'People' button at the bottom left-hand corner of Outlook (where you see Mail, Calendar, People and Tasks)

2. After double clicking, the user's email address you are having problems sending to this 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 by Rich Text Format.

Resolving at the Senders Server Level

This will need to be passed onto the senders IT Department.

When the Egress Gateway receives the email from the Exchange, it wraps everything up in a .switch file and occasionally a Winmail.dat attachment is included. Unfortunately, in certain instances, the Exchange may not be able to process the email correctly (a known issue with Microsoft -http://support.microsoft.com/kb/278061) before passing it on to Gateway.

The attachment seems to be lost already before Egress Client processes the message for encryption. As the linked article suggests, it could be a variety of reasons so we have come up with the following suggestions:

  1. We encourage you to look at whether these senders are using RTF instead of the default HTML formatting or any of the causes listed in that article. This can even be on a per-recipient basis, ie. it will send as RTF to a specific person.

  2. Changing an attribute in the actual contact on the Global Address List may resolve the issue, below are a number of screenshots and steps for each version of Exchange:

 Exchange 2007/2010:

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



Exchange 2013:

  1. Open Exchange Management Shell.
  2. To see your current settings please run the following command:

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

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

    Set-RemoteDomain -Identity DomainName -TNEFEnabled $false


If you experience this issue please contact your Systems Administrator who will be able to resolve this issue.

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