Re: What's happening to Sender: headers?

> On Apr 14, 2024, at 3:33 PM, Andrew Reilly <areilly@bigpond.net.au> wrote:
> 
> 
> Over the weekend I got around to investigating, and discovered that the errant messages don’t _have_ a Sender: header.  There’s a Return-Path: header that captures the envelope-from, but I haven’t figured out how to make sieve check that yet: it doesn’t seem to like it.  Sieve documentation is spectacularly inconclusive, but I suspect that the envelope extension might do what I want, but that’s not really my question.
> 
> Does anyone know why the Sender: header, which used to be so reliable that I had thought it an intrinsic part of the SMTP/MTA ecosystem, has gone away, or is at least not ubiquitous?

The Sender: field is optional. I don't know why FreeBSD stopped using it but I filter on List-Id: (which is used by pretty much every mailing list), which seems more appropriate.