Winmail.dat hides in your autocomplete

Here’s one of those technical blog posts that I’ve been meaning to post for a while now, but did not have the chance to do. Since I’m sitting here in the Baltimore airport next to a German-looking girl with extremely long hair, I’ve decided to work on the blog post so I do not appear to be admiring her hair.

On one of my visits to a NASA center, I was asked to look at a desktop situation that had really, really puzzled the local desktop techs. They had migrated the user to our mail system from the legacy system. The profile had been converted over to the new mail system, rather than a full wipe and reload of Outlook settings and whatnot (like we recommend).

THe problem was that no matter what she did, the user’s messages went out to certain people using the infamous Outlook rich-text format. This was producing winmail.dat attachments and was giving our mail system a really bad name. User perception is another issue… another day, another blog post.

Anyway, go read this if you don’t know what I’m talking about. This article describes the TNEF attachment situation and what to do about it.

Mainly, to stop winmail.dat attachments coming out of your Outlook users, you’re told to do the following:

  • Check Tools/Options/Email Format is not set to use Outlook rich-text (use HTML or plain text).
    • Check the contact entry for the receiver in your Contacts folder. Make sure they are not set to receive rich-text from you only.
      • Check your Exchange system mail paths to make sure that there are no conversions taking place at the server level. Even after checking all of this information, this user was still sending winmail.dat attachments to certain users. It was incredibly annoying. I asked her to demonstrate how she picks the user from the list to send a message. I noticed that she uses the autocomplete feature. She types the first few letters of the person’s name, then arrows down and hits enter to choose the autocomplete entry. After sending the message, the receiver still receives a winmail.dat.

        I took over the keyboard and started over by typing the name, then I arrowed down and hit DEL to delete the autocomplete entry. I then had her choose the recipient from the GAL again on the next message, which recached the entry from the GAL.

        Surprise… no winmail.dat.

        That’s right folks – if you’ve been all over hell and high water looking for what is setting your messages to send a winmail.dat, try removing the autocomplete entry. It appears the autocomplete entry stores this preference.

        Of course, I don’t recall Microsoft mentioning that fact. They probably don’t even know.