DKIM Setup In SMTP account

Step 1: Go to Settings -> Email Accounts -> click on the email address for which you want to setup DKIM

Step 2: Click on "Configure DKIM Signature"

Step 3: Click on "Generate DKIM Record" to see your DKIM DNS record settings

Step 4: Follow the instructions provided and setup the DKIM TXT record in your domain hosting site's DNS Settings.

Step 5: Once you have updated your DNS accordingly, wait for a few hours, and then come back and click "Check DKIM record & Save".