Segree, Gareth
>
> I have the following in my exim.conf
>
> acl_smtp_rcpt = acl_check_rcpt
>
> begin acl
>
> acl_check_rcpt:
> accept hosts = :
> deny message = This message contains an unwanted file
> extension \
> ($found_extension)
> demime = pif:exe:com:scr:vbs
>
> But I received an error (I have exim-4.20, do I need 4.22 for
> this to work)
> error in ACL: unknown ACL condition/modifier in "demime =
> pif:exe:com:scr:vbs"
Sounds like you have not applied the exiscan-ACL patch...
http://duncanthrax.net/exiscan-acl/
You need to patch the Exim basic package to use that type of functions.