Attachment blocking

Hi

we have only recently had the problem that when peeps send mail to us with attachments
they will get an undeliverable

with the following error

[Attachment denied by SHG SMTP proxy (type “application/octet-stream”, filename “download.exe”)]

however I will not always block it

is there any info on hacking the registry to enable this. if 3rd party software such as MIMEsweeper was used will it produce a similar undeliverable message

your in put is greatly apreciated