Quick post to let you know that Internet Explorer 8 is causing slow rendering problems in Notes clients, at least with version 8.0 and 8.5. And by slow, I mean up to 50 seconds to render any HTML email. Have not tested with any other Notes client versions.
If you revert back to IE7, all is normal.
No firm information as to the exact cause, but others are experiencing the issue, including one of my customers.
I am not aware of any configuration settings in Windows, IE, or Notes to effect this. Currently, the recourse is to revert back to IE7.
So, look out for any IE8 installs!