Michael Moser wrote:

Puzzled I investigated further and found that in Explorer under Tools
= Folder Options... = File Types the entry for "(None] URL:MailTo
Protocol" contains the value
"C:\PROGRA~1\MICROS~2\Office10\OUTLOOK.EXE" -c IPM.Note /m "%1" (i.e.
in 8.3 notation).

If I change this entry to use long filenames, i.e.:
"C:\Program Files\Microsoft Office\Office10\Outlook.exe" -c IPMNote /m
"%1"

and then click on such a MailTo-URL then things work as expected, i.e.
Outlook starts up and opens a new email with the recipient already
entered.

But after the next reboot that darn value is back to
"C:\PROGRA~1\MICROS~2\Office10\OUTLOOK.EXE" -c IPMNote /m "%1"

again and and things don't work any more.

So:
1.) Who/what is changing this value back???

I don't know. I've wondered myself.

2.) why does the short (8.3) form of the path not work here?

Perhaps "MICROS~2" is not the short form of the "Microsoft Office" folder.
Open a command prompt window, change to "Program Files", then use "dir /x
/p" ro locate the short name of "Microsoft Office" and if it's not
"MICROS~2", change the Open field in the "URL:Mailto Protocol" file type to
use the proper short name.
--
Brian Tillman