When I went to that site, I only accessed it. I didn't sign in to a web mail, so the cookie I got was the normal thing they deposit on anyones pc.
But after messing around today on that site, I generated a few different cookies:

You need to login to your mail, close down, and then come back to CCleaner, making sure you launch (not run) CCleaner after you do the logging in bit for it to pick up any relevant cookies.
Move all cookies from that site across to the right pane, to save searching for the right one, and then see if your details are retained.
If this doesn't work, we can look elsewhere.