I tried with another conditional but it still has not worked

Hi there @Max Ping 

Thanks for sharing with the Community. 

This is likely because there isn't a time delay between the initial email and the conditional split which doesn't leave the customer with enough time to open the email before being evaluated by the conditional split. My recommendation would be to add a time delay after the first email but before the Conditional Split to provide the customer with enough time to open the email.

Another recommendation would be to use a conditional split where “Has opened email where subject equals x” is your filter.

Tks Alex

Let me try!