Magnto 2.3 Newsletter Queue not sending

Question

The newsletter remain in the "not sent" state. Cron Job is up and running and all mails work accordingly. newsletter subscribtion mails are sent as well.

magento/var/log/exception.log shows this obscure error:

main.CRITICAL: Error when running a cron job {"exception":"[object] (RuntimeException(code: 0): Error when running a cron job at /var/www/magento/vendor/magento/module-cron/Observer/ProcessCronQueueObserver.php:327, Error(code: 0): Call to a member function appendChild() on null at /var/www/magento/vendor/pelago/emogrifier/src/Emogrifier.php:1419)"} []

Any hints to solve the problem? thanks!

Answer 1

For the sake of completeness. The Problem occured due to some bad templating. Emogrifier could not create working html/css code. After clearing the queue at mysql-cli level with

DELETE FROM newsletter_queue WHERE queue_id = "{id}"

Mails are sent now..

Answer 2

I'm using Magento 2.4 It seemed my newsletters weren't sending, but:

In my case, even though I set correct Time Zone in my Magento Configuration, my server was changing the time I entered to 6 hours ahead. My solution is to simply set queue time selector 6 hours sooner, and then it is sent. My cron tries sending newsletters in queue every 5 minutes. Yours is likely different.