First, you will need to enable the DKIM from Plesk using the following steps.
- Login to the Plesk Panel.
- Go to Tools & Settings > Mail Server Settings (in the Mail group) and scroll down to the DKIM spam protection section.
- Tick on the Allow signing outgoing mail.
Once you have enabled the DKIM from Plesk, you can enable it for the Domain.
- Select the Domain
- Go to the Mail tab >Mail Settings.
- Select the Domain and click Activate/Deactivate Services
- Select Enable for DKIM spam protection system to sign outgoing email messages and click OK.
Note: The DNS service must be activated on a domain and it must be using the Plesk DNS.
Plesk will automatically add the following two records to the DNS zone of the domain. Hence, you don’t need to add the record in the DNS Zone.
default._domainkey.<example.com> - contains the public part of the generated key.
_domainkey.<example.com> - contains the DKIM policy.
If domain is not using server's DNS, it requires to add necessary TXT records in the DNS zone of that domain.