Since then I have made many changes to my copy of the script. I did not redistribute it yet because I made some changes yet again to the column names and to the script name. These make necessary to edit saved layouts and tool tips. I am fine with doing it, but I don't know if you guys are willing to follow along every time I make a change.
What I have now:
Handling of mht/htm files. (Columns for Webpage Subject, Webpage Date, Webpage Source, Webpage Address, Webpage Domain.)
File format recognition depends on two Opus groups that should be created (Electronic Mail and Webpages). (Instead of hard-coding the extensions on the script, these groups are used.)
Handling of subjects broken over multiple lines. (Limited, there is one corner case not covered yet.)
Other small fixes and improvements.
Except for a problem with Windows Search (link to thread), the script seems to work fine. There is a copy of it in that thread, if anyone is willing to test it.
Because of all these changes, I think it would be better for me to release it on another thread as a version 1.0. Let me know of what you think about that.