554 5.7.1 <admin@contractingbygsc.com>: Relay access denied

554 5.7.1 <admin@contractingbygsc.com>: Relay access denied

Hello,

Im having issues with sending and receiving emails through Zoho Mail. Domain is contractingbygsc.com. At times im able to send mail (was able to send twice only) and at times i can receive the email (which was once). I tried sending from my personal Google email where i got this error.