How to parse ${__user.email} to get the username?

[zhouchi]

REGISTERED_COUNT{user=“user1”}
REGISTERED_COUNT{user=“user2”}

If the value of ${__user.email} is user1@domain.com and there are above two series in Prometheus, how to modify the following Metrics expression to get user1’s data?

REGISTERED_COUNT{user="${__user.email}"}