question about filtering spam

[Jan-Kees van Kampen]

hello list,

I wonder how it would be possible to filter a particular spam,
it's not triggering scores, but so omnipresent that I suspect more
people have had to deal with it one way or another.

I'm not sure if this is the right place to ask,
and please tell me if I should go elsewhere with my question :)
(I use postfix with clamav and spamassasin)

Anyway, I found that the pattern is rather simple:
attachments always have extensions .zip or .docm/docx
attachments' filenames always contain username of recipient

in pseudo code smth like this perhaps:

if
    msg contains attachment and
    attachmentname contains recipient-address.split($@)[0] and
    attachmentname.split($.)[1] == ".zip/.docx"
then
    trash / quarantaine ...
else
    pass through

So, I wonder how would one go about adding that sort of filtering..
Maybe this is simply available already ?

thanks for your attention,

Jan-Kees van Kampen