You can check an account's status from your Account Manager Admin Section.
From the left navigation menu, click Org or Team Tools > Accounts.
Search for the account you'd like to check.
To the right of the account, under the "Email Valid" heading, linked email addresses are displayed with a green checkmark. Email addresses that are not linked will have a red X.
For those who are not yet linked, click on the person's name. You can trigger a migration by clicking Email Login Instructions > Click Again to Confirm.