If you use MS Outlook, you may have received a bounce message with a subject containing:

BANNED: multipart/mixed | application/ms-tnef,.tnef,winmail.dat

or similar.

The bounce occurs because MS Outlook has sent an attachment named "winmail.dat" - even though you never intended to send any attachment. The winmail.dat attachment is readable only by recipients who also use MS Outlook; recipients who use other e-mail software, such as Mozilla Thunderbird can't read it, nor can virus scanners.

Winmail.dat attachments usually contain formatting information (bold text, etc.), but MS Outlook may pack other attachments also within winmail.dat attachments, such as viruses and other executables which can harm recipients' computers.

You should disable MS Outlook from sending winmail.dat attachments as follows:

• Select Tools > Options... from the menu.

• Go to the Mail Format tab.

• In the Compose in this message format: menu make sure either HTML or Plain Text is selected.

• Click the Internet Format button

• Make sure either Convert to Plain Text format or Convert to HTML format is selected under "When sending Outlook Rich Text messages to Internet recipients, use this format:" Make sure you DO NOT select "Send using Outlook Rich text format"

• Click OK.

• Click OK again.

Last modified 2007-12-12 18:10:11.