mime file as email attachment

Lately when users access their email, they get an attachment listed as “mime.—–“. Sometimes there are two or three copies of this “file”. When opened they find that this file is a copy of their local directory tree. This is not a constant thing but happens every once in a while. Any ideas?
The system is Dell 450Mhz machines, with NT4.0 on a Novell 4.11 network.