Outgoing email is blocked

Outgoing email is blocked

Need to get my account unblocked ASAP so that I can continue working. I had some messages bounce back last week after sending out a newsletter. I have submitted several requests directly through support through the day but I have not heard back indicating this has been 'unblocked.'

Could someone please address this issue and help me get it resolved?

Reason:Authentication failed:554 5.1.8 Sender Address Blocked