[exim] Creating autoreply in utf-8

Hello list,

I'm creating an autoreply transport. It's working well on my older
machine, which uses an ISO-8859-1 character set, but on the new one, the
whole database is in UTF-8, so I should generate the autoreply message
in utf-8. Here is the transport I tried:

vacation_autoreply:
        driver = autoreply
        to = ${sender_address}
        from = "${local_part}@${domain}"
        subject = ${lookup pgsql {PGSQL_Q_AWAYSUBJECT}{$value}}
        text = ${lookup pgsql {PGSQL_Q_AWAYTEXT}{$value}}
        headers_add = "Content-Type: text/plain; charset=utf-8"

However, as I know, the headers_add adds the header to the original
message, not the generated one. Is it possible to add the header to the
generated message?

Regards,
Gergely POLONKAI