That's the place I know how to look
It currently says:
Html editor: Notepad
E-mail: Microsoft Outlook
Newsgroups: Outlook Express
etc.
No mention of Lotus anywhere.
I did one of those finds on any file (that was less that 100K size- kept failing else) on C: that contains "mailto". Found a couple ini files that did not seem to be directing anything to Lotus. I'm guessing it is hidden somewhere in the registry, but I don't have the chops to find & fix it.