Re: [exim-dev] Use transport_filter

> transport_filter = '${if eq{$a}{$b}{/etc/exim/test.sh ${message_id}{}}'

Read documentation for transport_filter and
http://exim.org/exim-html-current/doc/html/spec_html/ch-the_pipe_transport.html#SECThowcommandrun

Also, you missed one }