Plesk

If you want to enable DKIM keys all Plesk subscriptions run the follovwing command in terminal:

for domain in $(plesk db -Ne 'SELECT name FROM domains WHERE parentDomainId=0;'); do plesk bin domain_pref --update $domain -sign_outgoing_mail true; done

1. Log in the Plesk admin portal, and navigate to Home >> Tools & Settings.
2. In the Security group find the SSL/TLS Certificates menu and click it.
3. Under List of certificates in server pool section click the Add button
4. The Upload the certificate as text section upload the KEY, CRT, and -ca.crt, and click the Upload button.
5. In the List of certificates in server pool section check behind the new certificate checkbox, and click the Make Default button
6. Next step, go to the Home >> Domains menu, and search the default server domain name, then click the domain name.
7. In the summary page find the Hosting Settings link, and click it.
8. Under the Security section, select the newly installed certificate, and click the Apply button.

Thats it.