So, the question is rather why Jesse and Michael's messages contain a Reply-To: header, and not yours. (What will my contain? Surprise surprise! Using Outlook)
While we're here blaming Outlook for things it might or might not do properly, it's simply insane that it let senders be impersonated in such an easy way: [cid:image001.png@01D4D8A8.4D8A1F70] (Subject's prefix and body's banner are due to a custom Exchange Transfer Rules in 0365, without it the message would have gone straight to inbox) The headers are: From: "no-re...@sharepointonline.com" <redacted@dayjob> To: <redacted@dayjob> There's no option in Outlook to display the sender's address along with (or instead of) the sender's name. -- Benjamin From: mailop <mailop-boun...@mailop.org> On Behalf Of Neil Jenkins Sent: mardi 12 mars 2019 02:44 To: Mailop <mailop@mailop.org> Subject: Re: [mailop] Mailing list with From header munging... and Outlook On Tue, 12 Mar 2019, at 09:26, Jesse Thompson via mailop wrote: When someone reply-alls to a munged message it only composes a message to the Reply-to and the Cc, but ignores the From (the list address is munged into the From header). That sounds exactly what I would expect for "Reply All"; it's certainly what's implemented at FastMail. * Reply => message is "to" either the Reply-To address if specified, otherwise the From address. * Reply All => Contents of To/Cc of message being replied to are also added to the new email (except for your address). I would be very surprised to see a client add both the From and Reply-To address as recipients on reply-all. Let's see what RFC5322 says<https://tools.ietf.org/html/rfc5322#section-3.6.3>: When a message is a reply to another message, the mailboxes of the authors of the original message (the mailboxes in the "From:" field) or mailboxes specified in the "Reply-To:" field (if it exists) MAY appear in the "To:" field of the reply since these would normally be the primary recipients of the reply. If a reply is sent to a message that has destination fields, it is often desirable to send a copy of the reply to all of the recipients of the message, in addition to the author. When such a reply is formed, addresses in the "To:" and "Cc:" fields of the original message MAY appear in the "Cc:" field of the reply, since these are normally secondary recipients of the reply. Yes, that sounds about right. Neil.
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