I have disabled the domain mccomplex.in completely in ISPConfig.
When you disable a domain then you instruct postfix that you dont want tto receive emails for this domain, this is not disabling sending as the sending can be done even trogh a completely different domain when the user is authenticated with correct username and password. To stop it you just have to disable the account that is used for sending or change the password of that account. Find out which email account is being used to send these emails and then disable this account. You can see this in the mail log file as there must be a smtp login right before the sending starts.