Well, I’ve experienced this first-hand as well.
But when I got to installing Windows Live Mail 2008 for my Hotmail needs, clicking on Messenger’s e-mail inbox button does open Windows Live Mail (or focuses its window if already open), and from just testing the e-mail sending thing, it also opens the Windows Live Mail New Message window. with the specified contact’s email in the To field.
I have a feeling this “bug” is caused either by Messenger trying to call Windows Live Mail, and if its program file is not found, crashes in failure of attempting to open it anyways, or Messenger using the MSNP URL command as a fallback, then tries opening the /unused* paths Escargot returns and crashes as a result of the URLs given not being valid HTTP URLs.
Anyways, I’ve decided to extract the Windows Live Mail MSI from my computer, since I used a copy of the original Windows Live 2008 installer to install it, and pack it in a ZIP file for you to install and configure (its too big for Discourse to upload, so here’s a Dropbox link instead):
Then you can follow @iGiftedSpade’s useful instructions for configuring it post-DeltaSync discontinuation here (it’s for Windows Live Mail 2012, but I’m sure you can accommodate it for Windows Live Mail 2008 for the time being).