A recipient who uses a non-Outlook email client, such as Apple Mail or Gmail, receives a file named winmail.dat instead of the actual document. The recipient cannot open this file.

This happens when you send with the Zivver Office Plugin or the Zivver OWA add-in.

Cause

Known Outlook and Exchange behavior causes this problem. It is not specific to Zivver or to the encryption of your message.

Outlook and Exchange can send a message in Rich Text format (TNEF). Outlook wraps the attachments in a single winmail.dat file. Non-Outlook email clients cannot unpack this file.

Changing the format in your own Outlook to HTML or plain text is often not enough. The format setting for the recipient or for the recipient’s domain determines which format is used.

Solution

Choose the solution that fits the scope of the problem. Solution 1 is recommended, because it applies to all users and to both the Office Plugin and the OWA add-in.

Solution 1: Disable TNEF for all external recipients (Exchange Online)

1. Connect to Exchange Online.

Connect-ExchangeOnline

2. Check which remote domains exist.

Get-RemoteDomain | Format-Table Name,DomainName,TNEFEnabled

3. Does no remote domain exist for all external domains? Then create one.
   Skip this step when a remote domain with domain name * already exists. Use the name of that remote domain in the next step.

New-RemoteDomain -Name "External" -DomainName *

4. Disable TNEF for the remote domain.

Set-RemoteDomain -Identity "External" -TNEFEnabled $false

5. Verify the setting.
   The value of TNEFEnabled must be False.

Get-RemoteDomain -Identity "External" | Select-Object TNEFEnabled

Solution 2: Disable TNEF for one contact

Use this solution when only messages to one specific external recipient are affected.

1. Connect to Exchange Online.

Connect-ExchangeOnline

2. Disable Rich Text format for the contact.

Set-MailContact <email address> -UseMapiRichTextFormat Never

Solution 3: Disable TNEF on one user’s computer

Use this solution when the problem occurs for one user of the classic Outlook only. This solution does not apply to the new Outlook or OWA.

1. Open the Windows Registry Editor on the user’s computer.
2. Go to HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Preferences.
3. Create a DWORD (32-bit) Value named DisableTNEF.
4. Set the value of DisableTNEF to 1.
5. Restart Outlook.

Alternatively, ask the user to change the format of new messages in Outlook.

1. Ask the user to open File > Options > Mail in Outlook.
2. Ask the user to set Compose messages in this format to HTML or Plain Text.

Note

The setting for a recipient or domain, such as the remote domain or the contact setting, takes precedence over this setting in Outlook. Does the problem persist? Then use Solution 1 or 2.

Workaround for the recipient

Does the recipient need the attachment immediately? Then the recipient can open the winmail.dat file with a free TNEF viewer. Use this workaround only temporarily, while the setting from the solutions above rolls out.

Still need help?

If you cannot find a solution, contact Zivver Support and include this information in your request:

• Which email client does the recipient use?
• Do you send with the Office Plugin in the classic Outlook, or with the OWA add-in in the new Outlook or OWA?
• Does the problem occur for one recipient, one domain, or all external recipients?
• Which steps from this page did you try, and what was the result?