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The order of priority for finding an existing user is as follows. If a different implementation is required, it must use a custom integration (see next section):
1) UserName - Unique, generated by code. Never able to update or change.
2) OrgLoginID - If an OrgLoginID is found, but the email is different; the email could be updated. TODO Clarify and update with logic.
3) Email - If an email is found, but doesn't match the OrgLoginID, an error is generated.TODO update with Matrix
Default Existing User check:
Custom Integrations and Custom CSV Formats:
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