Viewing a message in /mail/ should explain all the reasons each recipient was included on the message.
This is a whole lot of work but the alternative is fishing expeditions through application features.
Original Description
On our private install, I received the following email:
Date: Mon, 14 Sep 2015 11:54:47 +1000 To: josh@mydomain.com From: "User A" <phabricator@mydomain.com> Reply-to: T26779+24+5fe0121e81679d52@phabricator.mydomain.com Subject: [Maniphest] [Updated] T26779: REDACTED Message-ID: <61a94cf30e6a613af9646d79c4dc7d69@localhost.localdomain> X-Priority: 3 X-Phabricator-Sent-This-Message: Yes X-Mail-Transport-Agent: MetaMTA X-Auto-Response-Suppress: All X-Phabricator-Mail-Tags: <maniphest-projects> Thread-Topic: T26779: REDACTED X-Herald-Rules: <29>, <26> X-Phabricator-Projects: <#project_one>, <#project_two> X-Phabricator-To: <PHID-USER-fplpdm5kzihjdjndb6ql> X-Phabricator-Cc: <PHID-USER-fplpdm5kzihjdjndb6ql> X-Phabricator-Cc: <PHID-USER-hff4bjlxuuo5n27uuaat> X-Phabricator-Cc: <PHID-USER-abzwhc667osh5mwd4gk7> Precedence: bulk In-Reply-To: <maniphest-task-PHID-TASK-qkkj25dgcadxcktq4jlb@phabricator.mydomain.com> References: <maniphest-task-PHID-TASK-qkkj25dgcadxcktq4jlb@phabricator.mydomain.com> Thread-Index: YTBmMmMzZjVhMDVhYTIzNzRiODhjZjJlNWQyIFX2KOc= MIME-Version: 1.0 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=mydomain.com; i=@mydomain.com; q=dns/txt; s=mail; t=1442195687; h=Subject : To : From : Date; bh=aHov4ld5zVxvkLoXMdJ3Y77H0Gum08xpg6nfguy9m5M=; b=aNyM0PMLUJ7FF6M8Xsb1e5yVanRIhzEoqrQdBkrY6+RRvFMaIHXpeJBIPDqyxg24BWYloT rHxk0r7ppDsmSsUdjjeAHJ0/ewdUI4RO0NhwmGxVGhIsurL/GqrN7ujBBpb1NOkWqQjiZ92D W3FpsSMQ+bTBp8EDroWkkVj1lA91A= user_a added a project: #project_one. TASK DETAIL https://phabricator.mydomain.com/T26779 EMAIL PREFERENCES https://phabricator.mydomain.com/settings/panel/emailpreferences/ To: user_a Cc: user_a, user_b, user_c
When I navigate to the task, however, user_b isn't a subscriber. There are no transactions which act on user_b either.