Hello,
The details of extensions that needs to be blocked is in the file
/etc/antivirus.exim
Here is the part of code that do it:
----
# Look for single part MIME messages with suspicious name extensions
# Check Content-Type header using quoted filename [content_type_quoted_fn_match]
if $header_content-type: matches &(?:file)?name=(\&[^\&]+\\\\.(?:ad[ep]|ba[st]|chm|cmd|com|cpl|crt|eml|exe|hlp|hta|in[fs]|isp|jse?|lnk|md[be]|
ms[cipt]|pcd|pif|reg|scr|sct|shs|vb[se]|ws[fhc])\&

&
then
fail text &This message has been rejected because it has\n\
potentially executable content $1\n\
This form of attachment has been used by\n\
recent viruses or other malware.\n\
If you meant to send this file then please\n\
package it up as a zip file and resend it.&
seen finish
endif
# same again using unquoted filename [content_type_unqu
-----
Remove the corresponding entries of the extension and it will work.
Thanks