Bad filename in attachment

The message contained an attached file with a name we have blocked.

This may indicate a file type we have blocked, a specific name used in a virus attack, or a construction of a type the can be used to deceive the recipient as to the file type e.g. something.doc.zip or something.exe. In the last case you can try changing the name of the file before attaching it - change the ".exe" to something else and let the recipient know what you have done.