Prevent 'Portal only' customer and 'Atlassian account' customer with the same email address from co-existing

Problem Definition

Currently, it's possible for a 'portal only' customer and an 'Atlassian Account' customer with the same email address to be existing in the same service project.

This becomes an issue when the user creates an issue from the Help center portal while logged on to the 'portal only' customer and later replies to the email. Since both customer accounts have the same email address, when Jira receives the email from the user, Jira assumes it's the 'Atlassian Account' customer and creates a new request via email request.

Suggested Solution

When there are accounts with the same email address, have a mechanism to detect them and automatically disable the 'portal only' customer counterpart.

Workaround

Manually delete Jira Service Management portal only customers via https://support.atlassian.com/jira-service-management-cloud/docs/delete-a-customers-account/

--or--
Migrate portal only customer to Atlassian Account (two accounts will merge and request data will also be merged) https://support.atlassian.com/user-management/docs/manage-jira-service-management-customer-accounts/