Zoho rejected email sent from SendInBlue with 554 5.2.3 MailPolicy violation Error delivering to mailboxes

Zoho rejected email sent from SendInBlue with 554 5.2.3 MailPolicy violation Error delivering to mailboxes

Hi,

I am using Zoho email server for my SendInBlue account, to send transnational emails for my web app. Yesterday, 09-04-2020 19:47:43 my email sent by SendInBlue was rejected with 554 5.2.3 MailPolicy violation Error delivering to mailboxes.  Email size was around 50KB, so I do not see why this would happen. Can you tell me what seems to be the problem and how I can fix this.

Thanks