Correct.
You can send the turn from within the game. After you've opened the turn you received by double clicking on it in the email, when you've played your turn but before you end it hit alt-d. This will bring up your player details, where you can enter the smtp address of your isp in the appropriate field. No passwords for isp access, etc. Enter your email address while you're at it.
Your smtp address for your isp should be available from their email setup webpage, or if you have Outlook or similar going you'll be able to find it in your account settings for isp-based email accounts.