Unable to send message;Reason:554 5.1.8 Sender Address Blocked

Unable to send message;Reason:554 5.1.8 Sender Address Blocked

my email sending is blocked and i get the message Unable to send message;Reason:554 5.1.8 Sender Address Blocked. 

my email is support@appdimes.us

i only used this email to send the activation email to new members of my website. i have never done any kind of spam.

Now i cannot function my website because of this problem. this happened 2 days ago and i sent an email to support and filled the support form as well. but i didn't got a single reply so far.

I was planning to upgrade to premium but now im thinking to switch to some other email service. if this happens again, that will hurt my business.

for those who read this, think twice before selecting zoho for your business. they block email accounts without a single notice and offer terrible support