Per the domain verification documentation, when an organization admin un-claims a domain in Atlassian (manually or by un-integrating with GSuite), an email like the one below is fired off to all users under that domain:

We're writing to let you know that your Atlassian account is no longer managed by your Atlassian Cloud administrator.

This won't change the way you log in to Atlassian products or how you use them.

For more info, see Personal and managed accounts.

Admins may want the ability to disable those notifications or have them show up in product rather than email end users.