You can use DKIM by adding a TXT record to a subdomain. If you are using Google as your email provider, that subdomain will likely be "google._domainkey". The actual values will be given by your email provider.

To enter in the record, please follow these steps:

1. Sign in to your Dynadot account.
2. Select "Manage Domains" from the "My Domains" drop-down menu.
3. Check the box next to your domain name(s) and choose "DNS Settings" option from "Action" dropdown menu.
4. Choose "Dynadot DNS" option from the dropdown menu.
5. Scroll down to the "Subdomain Records (optional)" section.
6. Enter your subdomain in the box provided.
7. Under the "Record Type" section, select "TXT" from the drop-down menu.
8. Enter the value given by your email host in the "IP Address or Target Host" box.
9. Click on the "Save Settings" button at the bottom of the page to save your changes.

Your settings should look similar to what is shown here: