[exim] proper vacation processing

I am setting up new hardware to take over from my old service and am taking the
oportunity to clean up the exim configuration and remove lots of legacy issues.

My current service supports vacation using the Unix vacation program which derives
from University of California software. This does "the right thing" in only
responding to messages explicitly addressed to the user. It also does not respond
to messages from *-request, mailer-daemon etc.

I remembered having seen messages on this list from people using Exim's autoreply
for this, so decided to consider that instead.

However, the only examples I can find from searching the list archive seem to take
no steps to restrict the circumstances under which they respond. Indeed, the exim
spec (4.50: Section 46.8) makes no reference to this issue, particularly the risk of
creating a vacation loop between two people who have it set up.

In considering this problem I came to wonder if it is actually possible to do the
job properly without using an exim filter. For example, I can't seet at the moment
how I can check in a router if the recipients's e-mail address is in the To: or Cc:
header.

Phil.
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Phil Chambers (postmaster@???)
University of Exeter