Error: Unable to send message;Reason:554 5.1.8 Email Outgoing Blocked.

Error: Unable to send message;Reason:554 5.1.8 Email Outgoing Blocked.

Hello,
we already submited a request, but since we get no mail confirming the submission, we are reporting the problem here.
We are using mail on zoho for domain digitiup.com (zoho european mail server) and we can't send emails since last friday/saturday. Error is "Error: Unable to send message;Reason:554 5.1.8 Email Outgoing Blocked." We can't send mails for external domains or even to mail accounts using the same domain. We appreciate your resolve as soon as possible, since this is a critic situation and nothing was done on our side regarding configurations.

Kindest Regards,
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