Hi Viktor,

On 8/6/25 09:07, Viktor Dukhovni via Exim-users wrote:
# Exim filter
if personal alias [email protected]
then
   unseen mail
     subject "Automatic reply: $h_subject:"
     from "[email protected]"
     extra_headers "Content-Type: text/plain; charset=UTF-8"
     file ./.reply.msg
     once ./.reply
     once_repeat 7d
endif

This filter is not a good idea.  It appears to fail to take into account
the essential requirements of RFC3834:

     <https://datatracker.ietf.org/doc/html/rfc3834>

in particular the exceptions listed in:

     <https://datatracker.ietf.org/doc/html/rfc3834#section-2>

and ensuring that auto-reply envelope sender is the NULL sender: <>.

So unless those requirements are built-in features of the filter syntax,
this filter MUST NOT be used without appropriate modifications.

The docs say that the "mail" command has "no effect when the incoming message is a 
bounce (delivery error) message, and messages sent by this means are treated as if they were 
reporting delivery errors. Thus, they should never themselves cause a bounce message to be 
returned." 
(https://www.exim.org/exim-html-current/doc/html/spec_html/filter_ch-exim_filter_files.html#SECTmail)

And indeed, the Return-path: header of so-generated response messages is <> 
(I've checked). Assuming I'm understanding things correctly, this should take care of 
it.

Best,
Peter

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