I'm not aware of any issues with ironport.custhelp.com. If you are unable to get it to work, you may want to file a support ticket.
The secure items message is a browser warning and should be no different then when browsing direct to an HTTPS site that has HTTP objects on it.
In IE, this may be changed by Tools -> Internet Options -> "Warn if changing between secure and not secure mode". But I'm not entirely sure. You may be able to turn this off from the warning message itself as well.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...