For a while now some email sent from Wikipedia doesn't seem to arrive. Upon inspection this has been observed:
mx1001.wikimedia.org [2620:0:861:3:208:80:154:76] : SMTP error from remote mail server after RCPT TO:<wiki-huwiki-2-pgt2uv-CbZ/eQW6hVYDejbA@wikimedia.org>: 550 Administrative prohibition
There seems to be philosophical disagreement between the part generating the email (senders) in mediawiki and the mailserver config; possibly the mailserver should be fixed. Until then, these senders fail deliverability tests and the mail may get rejected.
This is an educated guess since I cannot be sure these are those email we're looking for since they haven't get delivered.