Quick question, in the marketing campaign record, I tired to create one and under the events subtab I created an email campaign, but no emails have been sent, I checked sent emails records, and there is an error. Must I verify the DKIM "Domain" or it's something else ??

@Mohamed Keno definitely check your DKIM config. If the Domain isn't validated, you can't send these emails. You'll need at a DNS record on the domain that you are trying to email from.