553 Relaying disallowed as xyz@yahoo.com (in reply to end of DATA command)

I configured my domain with postfix to use zoho SMTP server for sending outgoing emails , First two days all is good and I started getting athe following error

 550 5.4.6 Mail rate exceeded limit. <a href=https://mail.zoho.com/UnblockMe target=_blank>Click here</a> to unblock. (in reply to end of DATA command))

and fortunately it got corrected by itself in a day but started getting a different error for only some receipients as follows

553 Relaying disallowed as xyz1@yahoo.com (in reply to end of DATA command))

and also for my own system generated emails within my domain as follows

 553 Relaying disallowed as MAILER-DAEMON@mydomain.com (Mail Delivery System) (in reply to end of DATA command))

Please help