Check your address book entries for those who always get the dat files, and
make sure that the checkbox labeled always send in Rich Text format is not
checked. You'll see this checkbox if you double-click the person's email
address when looking at their Contact page.

-Peter

"Vince Averello [MVP-Outlook]" wrote in message
...
Are the recipients all using Outlook? If not, make sure you're not sending
mail in Rich Text Format

"C Brandt" wrote in message
...
Quick Question: About 10% of the people that I exchange emails with
cannot
open my attachments. They receive them as .dat files. If people have been
able to open an attachment from me, they can always open the attachments,
but someone who cannot read the first attachment I send to them will
never
be able to open an attachment from me.
Any clues?
I am running under Windows 2000 Service Pack 4 and Outlook 2000 SR-1 over
cable.