[exim] Newbie MIME ACL question

Hello all

I recently added .gif to list of banned filetypes in the MIME acl as our
answer to image spam. The reject message suggests that they zip it if
they really want to send it. We're seeing rejections which suggest that
this block is catching mailers using single pixel gifs as part of their
html formatting arsenal.

The examples seen so far have been tiny, so I thought perhaps we could
work around this by adding a second condition that checks that
$mime_content_size is greater than 1k like this

# File extension filtering.
  deny message = Blacklisted file attached ($mime_filename). Please zip
if needed.
        condition = ${if match \
                         {${lc:$mime_filename}} \
{\N(\.gif)$\N}{1}{0}}
        decode = default
        condition = ${if >{$mime_content_size}{1k}{1}{0}}

accept

I've obviously fundamentally misunderstood something because this lets
everything through! Could someone please point me in the right
direction?

Thanks

Mark Douglas


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Postmaster and System Administrator
Network Section
IT Department
School of Oriental and African Studies
University of London
Thornhaugh Street
London
WC1H 0XG