I found this, or the starters for this on here somewhere, but we have this

in sys_attachment, create a Before Insert Business rule

The condition is

parseInt(current.size_bytes) <= 1800 && current.content_type.toLowerCase().indexOf('image') != -1 && current.table_name.toLowerCase().indexOf('zz_yy') == -1 && current.table_name.toLowerCase() != 'sys_email'

and the script of

current.setAbortAction(true);


//gs.log(current.file_name + ' : insert aborted');

Cheers