To log your one-to-one emails using the forwarding address, your organization must allow external forwarding.
If your organization does not allow external forwarding, when you forward an email, you will receive this bounce back reply from your mail server in your inbox:
Remote Server returned '550 5.7.520 Access denied, Your organization does not allow external forwarding. Please contact your administrator for further assistance. AS(7555)'
To resolve this, talk to your IT department or your email administrator so they can modify your email server settings.