Got email blocked

Got email blocked

As a developer, I was configurating zoho smtp from my cloud server. 
I sent something like 15/20 email to the same address, and then got  ' noreply@yumami.it' blocked.
I receive this error: Error: Invalid login: 554 5.1.8 Sender Address Blocked

Can you enable it again and explain why it was blocked?
Thank you in advance,

Giacomo