How is winmail.dat my problem?

Misconfigured Outlook clients used to be the bane of my existance. And, occasionally can still be, in 2012. Which is pretty astounding, when you think about it.

The background is pretty simple, really. Outlook clients send e-mail using a Microsoft proprietary format, which certainly isn’t MIME. That is pretty amazing that someone thought that everyone, everywhere, would use Outlook to send mail to other Outlook users.

Try explaining to a customer that those files aren’t a Notes/Domino problem Sure, they understand,  but they want them to go away. So, it becomes my problem.

Thankfully, there are two notes.ini settings that you can apply to your SMTP server. Or server’s. Whatever the case may be.

Open the Domino Administrator. Go to the Servers tab, click on Server Console.

Enter “set config TNEFEnableConversion=1” then click either Send or hit enter.

Enter “set config TNEFKeepAttachments=1” then click either Send or hit enter.

To enable the setting to take effect immediately, enter “tell router update config” then click either Send or hit enter.

There, now someone else’s problem has been resolved on your servers. You’re welcome.

Here is a handy TechNote that explains the cause and resolution in a little more detail.

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