Configuration of domain DKIM records

[Marisa Paiva]

Good afternoon, 

We are trying to configure our domain's DKIM records as per article: 

https://confluence.atlassian.com/adminjiracloud/configuring-jira-cloud-to-send-emails-on-behalf-of-your-domain-979428371.html

But there is an error:As there's already a cname record used for the Sendgrid email platform, so we should refer to second bullet point of the same article:

If you're already using SendGrid to send emails from your domain for another service, you will not be able to add that domain a second time. In this case, it is recommended that you use a subdomain for your 'Project Email Address' setting. For example, use Jira@notifications.company.com instead of Jira@company.com.

Can you please clarify how to implement this subdomain? 

Thank you

Marisa