Lotus/IBM Notes allows users to receive emails with large attachments, which can encompass various file formats, including images, documents, spreadsheets, and videos. However, a commonly encountered issue involves attachments in the RTF (Rich Text Format), which are often displayed as 'Winmail.dat' and fail to show their correct format. In reality, these attachments are encoded messages containing both the plain text of the message and binary attachments in the 'winmail.dat' format. They typically contain the following information:

  • Only text of the message.
  • Embedded pictures and MS Office documents.
  • Custom features and special links and buttons.
  • Regular attachments.

Opening a 'winmail.dat' file in the existing application meant to handle the supposed attachments can be problematic, and there are several potential reasons for this issue.

Why this Winmail.dat Attachments Issue?

The attachment issue typically arises when the Exchange Server sends a message without enabling MIME encoding and opts for the proprietary Rich Text Format (RTF). It's worth noting that older versions of the Lotus Notes application do not support messages in the Rich Text Format. However, more recent versions, such as Domino 8.5x, have added support for RTF format.

You have two potential avenues for resolving this issue: you can either seek a solution through the Domino Administrator or explore options to modify the RTF formatting in various versions of the Exchange Server.

How to Resolve Winmail.dat Attachments Issue?

First, install the latest updates for Domino (versions 6.5.6, 7.0.3, 8.0.2, or 8.5.x).

Open your Domino Administrator. Navigate to SERVER > SERVER CONSOLE. Then run these commands one after another.

set config TNEFKeepAttachment=1

set config TNEFEnableConversion=1

tell router update config

Modify Exchange Rich-text Format Settings:
  • For Exchange 2003 :- Launch the Exchange Server Manager. Go to Global Settings in the Exchange System Manager, and then select Internet Message Formats and then click Standard.
    In the context menu, select Properties and click on the Advanced tab. Now under the heading "Exchange rich-text format" select 'Never Use'option and click on OK. Open the property of the domain and go to Advanced
  • For Exchange 2007 :- Open the Exchange Management Console. Then under Open Organization Configuration, select Hub Transport. Click on Remote Domains, then right click on Default Domain option and select Properties. Click on Format of original message sent as attachment to journal report option and click on the Message Format tab. Now within the Exchange rich-text format section at the bottom, select Never use and click on Apply.
  • For Exchange 2013/2016/2019 :- In Exchange Management Shell, run the following command to list the domains with RTF (TNEF) encoding.
Get-RemoteDomain | Where {$_.TNEFEnabled -ne $false}

Disable sending messages in RTF domain by running this command.

Set-RemoteDomain -Identity DomainName -TNEFEnabled $false

After executing the commands, you need to restart the Microsoft Exchange Transport Service to confirm the changes.

Configure TNEF conversion options

Mail senders can control the conversion options for TNEF messages sent to all recipients (both internal and external). The options available are:

  • Convert to Plain Text format
  • Convert to HTML format
  • Convert to Rich Text format Message format settings

By adjusting the RTF formatting settings, you can effectively address the WinMail.dat attachment issues in non-Exchange based email clients like Lotus Notes. If you encounter restrictions or limitations within your current Lotus Notes email client, consider migrating your data to any version of Exchange Server using the Kernel for Lotus Notes to Outlook tool. This software boasts a user-friendly interface and offers automated migration, ensuring a seamless transition. Feel confident in your ability to migrate your data securely and efficiently whenever the need arises.

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