Character encoding in autoreplies and vacation messages.

By default, no character encoding is specified for autoreplies or vacation messages.
If you'd like to define something, you can add this code:

headers = Content-Type: text/plain; charset="UTF-8"

into your uservacation and userautoreply transport sections of your /etc/exim.conf.  (not the directors, but rather the transports farther down in the exim.conf).

Adjust the charset value for the header as required.

Note, for the subject line, try this:

subject = "${if def:h_Subject: {Autoreply: "${escape:${length_50:$rh_Subject:}}"} {I am on vacation}}"

There are also reports of the use of $rh_Subject instead of $h_Subject working.

---

Another possible subject line:

 subject = ${if def:h_subject:
               {Autoreply: ${rfc2047:${quote:${escape:${length_60:$h_subject:}} }} }
               {Autoreply Message}
           }

Option 3:

 headers = MIME-Version: 1.0nContent-Type: text/plain; charset=UTF-8nContent-Transfer-Encoding: 8bit
 subject = ${if def:h_Subject: {Autoreply: ${quote:${escape:${length_50:$h_Subject:}}}} {Autoreply Message} }