Rocketman,
I do not think you can use INDEX_OF as part of a query.
There might be better ways to do what you want, but here is one way:
Use the EXE_SQL function like
EXEC_SQL `SELECT * FROM Members WHERE EmailAddress LIKE '%@%@%'` RETURN Members
If you are using the default AwareIM database, you will need to add your BSV name, followed by the under score (_), with the first Members like:
EXEC_SQL `SELECT * FROM BSV_Members WHERE EmailAddress LIKE '%@%@%'` RETURN Members
This will put Members with multiple email addresses into Context just like a FIND statement.