My fix described above failed when an iPhone user e-mailed to my dist. list and respondents clicking Reply ended up replying to just the sender and not the list.
Looking at his message headers, I found the message sent from an iPhone had an informal name before the email address in the "To: " field:
To: List Nickname <list@domain.com>
So I changed & simplified my regexp rule from this:
Code:
if /^To: <list@domain.com>/
/^To: <list@domain.com>/ PREPEND Reply-To: list@domain.com
endif
to just this line:
Code:
/^To: .*list@domain.com.*/ PREPEND Reply-To: list@domain.com
The 'dot-star' matches any number of any characters, and I put it before
and after the email address, so it also matches the angle-bracketed email address. That fixed the problem for me.
Of course, this would result in unwanted matches for email addresses like:
Code:
Joseph.List@domain.com
list@domain.commonserver.org
but my few sites have very few users, so the risk of false matches is low, for me.
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Update: revised entries in my postfix_header_checks.in 
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