IBM Support

Attachments to messages received from the Internet are named as winmail.dat

Technote (FAQ)


It has been reported that messages received from a Microsoft Exchange user containing an attachment arrive as a winmail.dat file attachment in the Lotus Notes client's mail file. These attachments are not able to be opened on the Notes client. Examination of the document properties reveals that the message was sent as a Content-Type: application/ms-tnef; name="winmail.dat".


This behavior is due to messages being sent from Exchange without MIME encoding turned on. Winmail.dat is attached to the message in uuencoded format. Information on how to prevent winmail data being sent to Internet users from MS Exchange is documented and publicly available from the Microsoft Support Web page, in the Microsoft Knowledge Base, article number Q138053.


An enhancement request was submitted to Quality Engineering and functionality to decode winmail.dat attachments was added to Domino release 6.5.6, 7.0.2 and 8.0.

Excerpt from the Lotus Notes and Domino Release 6.5.6 MR fix list (available at

    SPR# SBRN5PGPCN - This fix extracts attachments from TNEF streams. TNEF streams are sent from Microsoft Outlook users when the sender tells Outlook to send "rich text" to the recipient. The TNEF stream is a formerly proprietary Microsoft method for "tunneling" Microsoft Rich Text Format (RTF) data over the Internet. Microsoft has published the specification for the TNEF stream format. We now can decode TNEF streams (almost always sent as an attachment named 'winmail.dat') and extract any embedded file attachments. Any embedded file attachments are then attached to the message which is delivered to the Lotus Notes' recipients mail database.

To enable the fix a server notes.ini parameter must be used:

    NOTE: This parameter is associated with an issue with crashes that could occur in Domino 7.0.2 and 7.0.2 FP1 and was fixed in Domino 7.0.2 FP2 and later ( SPR# KTIS6VZHYR).

The fix also has some additional options:

-- This will keep the winmail.dat object as well as extract the regular attachments:
-- This will append a rich text entry containing the message body:


Workarounds for earlier releases
The sender can configure their client to avoid TNEF Encoding.

Related information

A simplified Chinese translation is available

Cross reference information
Segment Product Component Platform Version Edition
Messaging Applications IBM Notes

Document information

More support for: IBM Domino

Software version: 6.0, 6.5, 7.0, 8.0, 8.5

Operating system(s): AIX, IBM i, Linux, Solaris, Windows, z/OS

Reference #: 1093342

Modified date: 19 August 2013