That's not a popup
per se, it's an Information Bar prompt. According to what the IB prompt says, it's not allowing the use of an ActiveX control that's currently installed on the computer, so it would seem to be something you already have installed.
Note that you have the webmail site in your Trusted Sites zone, which is sort of the opposite of what I was suggesting you do. If you don't want IE7 to be able to download ActiveX controls, you want to disable ActiveX download in the Internet Zone, and
leave this website and others in the Internet Zone so the setting applies to them. The Trusted Sites zone would be for sites that you
do want to have ActiveX download options, e.g. Microsoft Update and such.
Big picture: find out the author of the ActiveX dealiebob you don't want, and block it at your router by keyword. For example, if I don't want Flash Player, I can block Adobe's download site at the router, and that's the end of that nonsense
