So I just found this error was occurring while I was checking the daemon logs for another issue:
[2015-12-16 16:12:34] EXCEPTION: (PhutilProxyException) Error while executing Task ID 1043154. {>} (SimpleEmailServiceException) SimpleEmailService::sendRawEmail(): Sender - MessageRejected: Email address is not verified. Request Id: 9d891c32-a3b3-11e5-8b6d-752ed81883f8 at [<phabricator>/externals/amazon-ses/ses.php:390] arcanist(head=hachquemaster, ref.master=9a373c88d747, ref.hachquemaster=9b8c9d280ea4), phabricator(head=72c95201798591195a1737c8d34ce52cffd38799, ref.master=1d72c97fc9f6), phutil(head=hachquemaster, ref.master=4a09be9ffd4a, ref.hachquemaster=c19c95a28452) #0 <#2> SimpleEmailService::__triggerError(string, array) called at [<phabricator>/externals/amazon-ses/ses.php:272] #1 <#2> SimpleEmailService::sendRawEmail(string) called at [<phabricator>/src/applications/metamta/adapter/PhabricatorMailImplementationAmazonSESAdapter.php:33] #2 <#2> PhabricatorMailImplementationAmazonSESAdapter::executeSend(string) called at [<phabricator>/externals/phpmailer/class.phpmailer-lite.php:496] #3 <#2> PHPMailerLite::Send() called at [<phabricator>/src/applications/metamta/adapter/PhabricatorMailImplementationPHPMailerLiteAdapter.php:104] #4 <#2> PhabricatorMailImplementationPHPMailerLiteAdapter::send() called at [<phabricator>/src/applications/metamta/storage/PhabricatorMetaMTAMail.php:733] #5 <#2> PhabricatorMetaMTAMail::sendNow() called at [<phabricator>/src/applications/metamta/PhabricatorMetaMTAWorker.php:26] #6 <#2> PhabricatorMetaMTAWorker::doWork() called at [<phabricator>/src/infrastructure/daemon/workers/PhabricatorWorker.php:122] #7 <#2> PhabricatorWorker::executeTask() called at [<phabricator>/src/infrastructure/daemon/workers/storage/PhabricatorWorkerActiveTask.php:171]
This should be surfaced (maybe as like a setup check warning if it's detected in the last 100 logs or so?) so that I know I need to go and fix my AWS SES configuration.