Cool, I didn't know that (started late 90s here) but that wasn't what this person attempting to do. Apparently she had asked for the source from another dev's script and saw something like:
action="process.php"
And just thought This Should Work™ too and put the mailto: into the form. When it happened, in front of 50 other people, I just stared at her for a moment and said it was complex and we could look at it later. Not really much else you can do in those situations.
No. Mosaic did not have an integrated email reader, and there was no protocol for starting your mail client of choice. OmniWeb did support mailto: by passing it over to the mail app on NeXTStep, but that was an uncommon platform.
When I first learnt HTML in the late nineties, the book I used contained mailto actions on forms, which I remember worked just fine for me in IE (4 or 5). Some searching suggests that IE interfaced with Outlook Express to do this.
