Can't send any emails with ZOHO writer (Error 1321 - Hard bounce email error)

Can't send any emails with ZOHO writer (Error 1321 - Hard bounce email error)

Hi everyone

can someone help to clarify this problem? I am trying to send a bulk of emails using a CSV file. Everything looks fine but the emails can't be sent out due to error 1321 (hard bounce error). 

I assume it has something to do with un non-existing DKIM record which I have asked our IT department to create, according to the instructions from ZOHO. 

Will the issue be resolved when the DKIM is created or could it be a different problem?

Thank you!
Erwin