Hi, @atmaarten!
Thanks for reaching out!
Please kindly know, that the DKIM record should be provided by the mailing service you’ve chosen.
The main purpose of the Easy WP SMTP plugin is to bridge a connection between your WordPress site and your email mailing service (chosen mailer). Simply put, Easy WP SMTP makes it so your site can send emails efficiently. Without the plugin, WordPress can still send email but it does it in a less reliable way. You may end up with emails going into spam or not arriving at all. With Easy WP SMTP, we connect you to an email service that helps to ensure that does not happen.
Please, follow our step-by-step guide on how to configure the mailer here.
And you’ll find the steps in the guide on how to add the DKIM record.
Kind regards.