So, just to be clear.. is this something you want to do in Cloverleaf ? Create a .ics file and send it to email recipients? Start with the entry in StackOverflow.com – search for “Outlook Calendar invitation file extension” and pick the entry that talks about .ics vs. .vcs file types. There is a reference to the RFC definition for .ics files.
Then you can use the SMTP and MIME packages in tcl and create the email with the .ics file attachment. This is theoretical. I have created emails in Cloverleaf tcls with HTML, PDF or RTF attachments and they work fine, so I imagine you can do the same with .ics files.