Timothy Luoma asked,
| My guess is that 'formail' is smart enough not to grab 'Sender:' if
| that is put down in RFC822, but perhaps it prefers the "From " line
| over the "From:" line when choosing addresses?
For a few versions there was a bug in formail that made it prefer From_ to
other header lines.
In version 3.11pre4, formail -r prefers Sender: to From: (incorrect for
sending a response to the text, but perhaps correct for acknowledging receipt
or otherwise reacting only to the event that mail came in) and formail -rt
prefers From: to Sender: (correct for responding to the text). Both -r and
-rt prefer Reply-To: to both From: and Sender:, but the message in Timothy's
example did not have a Reply-To: line.
The full table of precedences is in the bar graph in the formail source.
If your version of procmail is recent enough to include extraction (the
\/ operator), you can set up your own ranking for any given situation.