[Exim] mask:$sender_host_address in system filter

Sirs, one more question. I'd like to construct expression to separate lan
user's messages from messages, moved by system filter to spambox. (The
reason is that such messages doubles in outbox archive file)

So, as written in FAQ, i've inserted in system filter:

if $sender_address_domain is foo.bar
and ${mask:$sender_host_address/24} is 192.168.0.0/24
    then
     unseen save /usr/backup/test

but, when messages processed with exim4 -bf myfilter i've got error:

Filter error: failed to expand "${mask:$sender_host_address/24}" in filter
file: "" is not an IP address

What's wrong? And may be there is more 'clean' solution?


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Michael V. Sokolov, SA/Helpdesk