Unfortunately if DKIM is to be preserved, and the DKIM signature covers the Subject line (which it usually does), changing the Subject would break the signature and cause the bouncing problem to start happening again.
Looking at Warren's message at the beginning of this thread, I see the following DKIM signature:
DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=
tuhs.org; s=dkim;
t=1506828345; bh=JrrWTXe8/s8WUvyQhbjteoiXK8kMtqkyNHZyzoe+YwE=;
h=Date:From:To:Subject:List-Id:List-Unsubscribe:List-Archive:
List-Post:List-Help:List-Subscribe:From;
b=1bchv7u0p3glxS5aOdV2a2LcTPR/UNiVdxne762fZ8jTn8/PY6UDE0CEqfP1rS20G
t6uVy6iNk/xoDDKPeKGH4Tt8lSKqujoN682dKcAkHsM8/1ADamNo9ep/J7qiLUQIm7
62+lEKp7NZL8zsA2H+5iXtlcuKKIWJ3cTvhdhFLA=
This means that changing any of the headers listed under h= will break the signature (and cause bounces). This unfortunately includes the Subject.
For lists the alter the From: line, I prefer if they put the original From: address in the Cc: line as that means a reply-all goes both to the list and the originator. However I'm not sure whether this will cause DKIM issues as well (I haven't dug deep enough).
There's some discussion of this in RFC6377, unfortunately without a good solution given.
David
On Mon, 2 Oct 2017,
jason-tuhs@shalott.net wrote:
All else being equal, I would prefer the old list retain the old behaviour (i.e., to add the "[TUHS]" string to the Subject line) if possible.
Same. My mailbox gets a lot of input from a lot of places and I generally use the subject line to optically filter - the tag really helps.
-uso.