Email outgoing blocked

Email outgoing blocked

Hi, a domain we setup recently for emails.. one of the emails got blocked yesterday ( sales@whitemist.co), which I unblocked through the unblockme page, but it seems to be blocked again. I can confirm, we are not using Zoho to send out bulk emails .. but instead it's an e-comm store and sends out around 10 - 20 emails per day to customers as order confirmations. Or customer notes.

Wondering, what caused the block to happen so we can try and avoid that in the future. Pls see the screenshot I see, when I try to unblock the email -  https://www.screencast.com/t/njEkL3rzvED9

Thanks!