Add an optional configuration option to set 'Precedence: bulk' headers on

transactional mail

Summary: See T571. SES refuses to deliver mail with this header and there are
various reports of other issues on the internet so I'm defaulting it to off.

Test Plan: Set config to true, tried to send mail, SES rejected it because of
"Precedence: bulk" header.

Reviewers: bmaurer, ola, jungejason, nh, aran

Reviewed By: aran

CC: aran, epriestley, bmaurer

Differential Revision: 1032

conf/default.conf.php

@@ -279,6 +279,15 @@ return array(
   // address will be stored in an 'From Email' field on the task.
   'metamta.maniphest.default-public-author' => null,
 
+  // If this option is enabled, Phabricator will add a "Precedence: bulk"
+  // header to transactional mail (e.g., Differential, Maniphest and Herald
+  // notifications). This may improve the behavior of some auto-responder
+  // software and prevent it from replying. However, it may also cause
+  // deliverability issues -- notably, you currently can not send this header
+  // via Amazon SES, and enabling this option with SES will prevent delivery
+  // of any affected mail.
+  'metamta.precedence-bulk' => false,
+
 
 // -- Auth ------------------------------------------------------------------ //