550 message was classified as SPAM

After MailChannels was discontinued, the new email delivery system has become problematic.

Now, several domains are being prevented from sending emails because the error message 550 This message was classified as SPAM and may not be delivered always appears.

If you register an email to send a form in Elementor, you get this error. If you send an email through the cpanel webmail, you get this error.

Every day I have to create a support ticket requesting that an email be unblocked.