Sender: headers again

[fanf]

http://fanf.livejournal.com/44733.html

I just found out an explanation for Outlook's irritating behaviour that I was working around back in January. It turns out that Sendmail has never followed the standard's requirements for the Sender: header (it never adds or fixes it), so the developers of Outlook assumed that you would only see a Sender: header when the message had been transmitted via a mailing list. This makes the "from [list] on behalf of [author]" wording look relatively sensible. However, they should have used the bloody List-ID: which is supposed to be used for exactly this kind of thing.

What is worse is that Exim is out on a limb in this respect. Postfix used to follow the standard but was changed in 2000 to be bug-compatible with Sendmail. This is very irritating, because the standard behaviour is much more useful. Grr.

Comments

[http://users.livejournal.com/_nicolai_/]

I now hate Sendmail a bit more, while already hating Outlook a very great deal. I will soon be configuring my Exim MTA not to add the Sender: header because when our software at work running under the username USER1 emits email From: USER2 (typically USER2 == "support@companyname" so that replies go back to humans not sysadmins) and is read by people using Outlook they reply to USER1.

[mikewd]

I believe Outlook does honour Reply-To: so it makes sense to set this for Support@name type e-mails. (We do that and replies from Outlook users always seem to come back correctly addressed to support).

It is probably still a good idea to have some sort of header in the message to allow you to identify the real sender for troubleshooting purposes so it might be worth rewriting the "Sender:" header into some sort of "X-sender:" that is not going to be trivially visible in the recipients MUA.
(Anyone with enough clue to examine the full headers is probably sensible enough to send to the correct addresses...).