All email replies will go to the inbox (in Gmail, iCloud, etc.) of the email address that sent the message. You can find the sending email address by heading to the Messages page on the left menu > Click on your sent email > View the From email.
By default, the sending email address will always be the same as the user who sent the email in Clearstream. If you want to change your default sender, head to the Settings page from the left > Email.
