I've some problem sharing recipes.

On my computer I've both Outlook 2007, which I don't use, and Thunderbird and I use.
I've got two problems.
1- when I try to share a recipe, a new Outlook message is created with a text telling me that the attached file is used to download the feed, but no file is attached (see image)
2- is there a way to tell Calibre to use Thunderbird as a mail client? May be I've to uninstall Outlook?
Thanks