Hello,
For more than 2 years, we remind the need to use the smtp with authentication to avoid hacking emails sent by websites, and as a consequence a degradation of IP reputation causing mail delivery issues for legitime emails for all users of the concerned server.
This is no longer tolerated, it will soon be the norm for all web hosts and has long been in the obligations of our Terms.
It's up to you to correctly configure your website via its CMS or smtp php code. (Contact your webmaster if needed)
Reference:
Friday, September 28, 2018