Cursor cursor = context.getContentResolver().query(ContactsContract.CommonDataKinds.Email.CONTENT_URI,
            new String[] {Contacts._ID}, ContactsContract.CommonDataKinds.Email.ADDRESS + "=?",
            new String[] {email}, null);

Cursor cursor = context.getContentResolver().query(ContactsContract.CommonDataKinds.Email.CONTENT_URI,
        new String[] {Contacts._ID}, "lower("+ContactsContract.CommonDataKinds.Email.ADDRESS + ")=lower('"+ email +"')",
        null, null);

Cursor cursor = context.getContentResolver().query(ContactsContract.CommonDataKinds.Email.CONTENT_URI,
        new String[] {Contacts._ID}, "lower("+ContactsContract.CommonDataKinds.Email.ADDRESS + ")=lower('"+ email +"')",
        new String[] {}, null);

Cursor cursor = context.getContentResolver().query(ContactsContract.CommonDataKinds.Email.CONTENT_URI,
            new String[] {Contacts._ID}, ContactsContract.CommonDataKinds.Email.ADDRESS + "=? COLLATE NOCASE",
            new String[] {email}, null);