Hi,
Indeed, as Crowd is using the SecurityRealm API (same as LDAP), it’s not possible have multiple account with the same email.
With OAuth2, we’ve introduced a feature that allow a user to “steal” the email from another account (supposing it’s the same person as he’s using the same email), but nothing as been done for SecurityRealm.
To give more context, it’s not possible for the moment in SonarQube to have same email for multiple account because for the issue auto assign feature we need to find one user having the email from SCM.