[exim] Get original message_size before transport_filter

I have the following transport I'm using to try to work with message compression on Maildir store.

All seems to work ok, things get compressed, but Maildir file gets the size (S=) POST filter.

While it's compressed on disk, the uncompressed version is used on the mail client/MUA side.


maildir_tag = ,S=$message_size,W=${eval:$message_size + $message_linecount + 1}
transport_filter = /usr/bin/xz



Is there a way to get the $message_size BEFORE the transport_filter? Transport filter seems to modify the size to the actual new size, which in this case is not desirable.

Is there anything like "$orig_message_size" or would I have to get the message size earlier in the transport and set a macro? Maybe with a condition, but I'm not sure that will work since I think conditions are hit last?


TIA
-Robert