celery: drop config settings not supported in Celery 4 CELERY_SEND_TASK_ERROR_EMAILS has been removed, according to https://docs.celeryproject.org/en/3.0/whatsnew-4.0.html#features-removed-for-simplicity : "Tasks no longer sends error emails. This also removes support for app.mail_admins, and any functionality related to sending emails." The "ADMINS" prefix might be a left-over from the long removed celery.conf.ADMINS - last seen on https://docs.celeryproject.org/en/2.1-archived/reference/celery.conf.html#celery.conf.ADMINS . The "ROUTES" prefix might refer to "CELERY_ROUTES" ... but it doesn't take a simple string list anyway, so there is no point in treating it as a list value.

--- a/development.ini	Thu Feb 13 14:46:50 2020 +0100
+++ b/development.ini	Thu Feb 20 01:35:22 2020 +0100
@@ -257,7 +257,6 @@
 
 celery.result.backend = db+sqlite:///celery-results.db
 
-#celery.send.task.error.emails = true
 #celery.amqp.task.result.expires = 18000
 
 celeryd.concurrency = 2